Near the village of Carbury, the Doctor and Ace meet Brigadier Winifred Bambera of UNIT, who is overseeing a missile convoy. They are attacked by knights from another dimension in pursuit of the noble Ancelyn, who recognises the Doctor as the sorcerer Merlin. Stranger still, a spaceship hidden beneath the waters of the nearby Lake Vortigern conceals the fate of the legendary King Arthur. But the Doctor may have met his match when Mordred, commander of the knights, summons his mother, the mighty witch Morgaine. Fortunately, Brigadier Lethbridge-Stewart has arrived to stand at the Doctor's side one last time.

Writer Ben Aaronovitch and script editor Andrew Cartmel began discussing Doctor Who story ideas in early 1987. After false starts with “Knight Fall” and “Transit”, Aaronovitch suggested an adventure which would juxtapose sword-and-sorcery elements with a modern setting. Thinking especially in terms of the Arthurian legends, he felt that this could offer the opportunity to provide a scientific explanation for the mythology's magical events and characters. Although now generally regarded as a folkloric invention, King Arthur was supposedly a military leader circa the fifth century whose prowess on the battlefield was cited in both the ninth-century Historia Brittonum and the tenth-century Annales Cambriae. A tremendous number of associated stories developed during the second millennium, notably the works of writers like Geoffrey of Monmouth, Chrétien de Troyes, Sir Thomas Malory and Alfred, Lord Tennyson. Over time, elements such as the Knights of the Round Table, the sword Excalibur, and the wizard Merlin were popularised.

As the summer waned, Aaronovitch began developing ideas for his storyline, which won the approval of both Cartmel and producer John Nathan-Turner. Aaronovitch planned to include characters from the United States Air Force, and Nathan-Turner suggested that he incorporate the United Nations Intelligence Taskforce (UNIT), which had been prominent in Doctor Who in the early-to-mid Seventies. In turn, Aaronovitch inquired as to whether he could use UNIT's Brigadier Lethbridge-Stewart, whom actor Nicholas Courtney had last played in 1983's The Five Doctors. Aaronovitch was unhappy with the suggestion made in the same year's Mawdryn Undead that the Brigadier had retired from UNIT to teach maths, and he wanted to provide a more suitable end to Lethbridge-Stewart's adventures with the Doctor.

In Autumn 1987, Ben Aaronovitch was asked to set aside his Arthurian adventure to work on Remembrance Of The Daleks

In the autumn, however, Cartmel and Nathan-Turner asked Aaronovitch to set aside his Arthurian adventure in order to work on Remembrance Of The Daleks, which would serve as the Season Twenty-Five premiere. The earlier storyline was not forgotten, and Aaronovitch returned to it in the spring of 1988. At this point it became known as “Storm Over Avallion”, although “Lake Over Avallion” was also considered. It had originally been conceived as a three-part adventure to be made entirely on location, but Aaronovitch was now told to expand the narrative to four episodes, with some footage to be recorded in the studio.

Aaronovitch borrowed heavily from Arthurian folklore, including Arthur's half-sister Morgaine (also known as Morgan le Fay) and his bastard son Mordred. He followed the modern trend of portraying them as a villainous mother-and-son duo; in fact, both characters' motivations had evolved over the centuries, and their familial relationship was a product of a more recent conflation of Morgaine with another character called Morgause. Aaronovitch also planned to feature a revived A'tur (ie, Arthur) at the story's conclusion, whom he described as king of the Br'tons (rather than Britons). Ancelyn was inspired by Lancelot, one of the best-known of the Knights of the Round Table. Lancelot was perhaps most notorious for his affair with Arthur's wife, Guinevere, thereby suggesting Bambera's first name, the linguistically-related Winifred. Ace's retrieval of Excalibur from Lake Vortigern was an inversion of one of the legends which described how Arthur obtained the sword, in which it emerged from beneath the surface of a pond, offered to him by the mystical Lady of the Lake. Carbury itself was named for Cadbury Castle in South Cadbury, Somerset, which local tradition identified with the Arthurian Camelot.

At this stage, Aaronovitch retained the USAF element of the serial; Bambera was an American captain acting on behalf of a joint US-European initiative codenamed “Camelot”. Another key supporting character was Lavender Warmington, director of a heritage group called the Carbury Trust, while the Asian student befriended by Ace was named Thai. Ace wielded a newly-constructed sonic screwdriver, resurrecting the device used by the Doctor for many years until its destruction in 1982's The Visitation.

In the late stages of the narrative, Morgaine ensorcelled Ace and planned to sacrifice her. Otherwise, the demon she had raised would eradicate all life on Earth, thereby sealing the portal between this dimension and Morgaine's, trapping A'tur. Lethbridge-Stewart called in an airstrike against the demon, and was mortally wounded; his death satisfied the demon, who departed. Bambera killed Mordred to save Ancelyn, and A'tur awakened from suspended animation, offering to bring Mordred back to life in return for Morgaine's submission. Bambera accompanied Ancelyn back to his dimension, while the Doctor would continue travelling through time and space in honour of Lethbridge-Stewart.

Nicholas Courtney did not think Doctor Who would continue much longer

In September, Courtney -- who had recorded a cameo appearance as a tourist in Silver Nemesis at the end of June -- was approached about returning as the Brigadier. He agreed, and indicated that he approved of the plan to kill off his character. Given the BBC's attitude towards Doctor Who in recent years, together with its dwindling audiences, Courtney did not think the programme would continue for much longer and so he was keen to shepherd Lethbridge-Stewart's story to a close. With the actor on board, the scripts for “Storm Over Avallion” were commissioned on September 16th.

Aaronovitch then made various changes to his storyline. Bambera became a UNIT brigadier and the involvement of the USAF was removed, Thai was renamed Shou Yuing, Lavender Warmington's role was taken over by Peter Warmsly due to Nathan-Turner's concerns that there were too many female characters, and Ace's sonic screwdriver was dropped. Mordred was no longer killed, and the demon -- now referred to as a Death Elemental -- was able to reanimate dead knights to become his zombie-like servitors. The Brigadier survived the airstrike and slew the demon with Excalibur, only to be fatally injured by the resulting feedback. Concerns about the unpredictable nature of weather on location prompted Aaronovitch to rethink his title, with “Pool Of Avallion”, “Song Of Avallion” and “Stormtroopers Of Avallion” all considered.

By early 1989, Aaronovitch's story was intended to be the first into production for Season Twenty-Six. Nathan-Turner hoped to attract Graeme Harper -- who had directed 1984's The Caves Of Androzani and 1985's Revelation Of The Daleks -- back to Doctor Who for “Storm Over Avallion”, but he was unavailable. Instead, the director would be Nicholas Mallett, whose most recent work had been Paradise Towers in 1987. However, Courtney then advised Nathan-Turner that he had been offered a role in a West End revival of M Butterfly, for which he would be required during the planned April recording dates. As such, it was decided to interchange “Storm Over Avallion” with the next story on the production schedule, Ian Briggs' The Curse Of Fenric. Unfortunately, it then transpired that Courtney would still be unable to appear in both Doctor Who and M Butterfly, and he ultimately decided to turn down the West End opportunity. Courtney was contracted for his return to Doctor Who on February 14th.

Jean Marsh (Morgaine) had been the First Doctor's short-lived companion Sara Kingdom

Because of the changes to the production calendar, “Storm Over Avallion” would now be made by a director new to Doctor Who named Michael Kerrigan. Kerrigan had been recommended to Nathan-Turner by Remembrance Of The Daleks director Andrew Morgan, whom the producer had been eyeing for the job. The key piece of casting was for the sorceress Morgaine. This role went to Jean Marsh, who had been the First Doctor's short-lived companion Sara Kingdom in 1965's The Daleks' Master Plan, as well as Joanna in the same year's The Crusade. Marsh also had experience playing witches on the silver screen; she portrayed Mombi in Return To Oz (1985) and Queen Bavmorda in Willow (1988). Another connection to Doctor Who's early years was the presence of assistant floor manager Matthew Purves whose father, Peter, had been companion Steven Taylor in 1965 and 1966.

Meanwhile, Aaronovitch's scripts continued to evolve. Still searching for the right title, he offered “The Battlefield”, which Cartmel abbreviated to simply Battlefield. Aaronovitch had also wanted to promote Lethbridge-Stewart to General, but his rank reverted back to Brigadier. More significantly, Nathan-Turner and Cartmel now felt that the story was so full of incident that Lethbridge-Stewart's heroic death would not get the attention it deserved. Aaronovitch offered other alternatives, including one where the Brigadier survived and decided to accompany the knights back to their dimension. In the end, however, the production team preferred the version where he returned to his quiet life with Doris. Aaronovitch would subsequently regret the inclusion of Lethbridge-Stewart in his busy narrative, and would feel that he had not properly considered the impact of the expansion from three to four episodes.

Other changes were of a more logistical nature. Aaronovitch had indicated that Morgaine's demon, now called the Destroyer of Worlds, should initially manifest in the form of a well-dressed human man. Only after his bonds were shattered would he metamorphose into a monstrous form. To simplify the narrative, it was decided that the Destroyer would appear in the latter guise throughout. Similarly, the knights were intended to be dressed in futuristic combat gear which only looked like traditional armour at a glance, but this notion was dropped on the basis of cost.

Location filming for Battlefield began in Buckinghamshire on May 6th. In Fulmer, the garden centre was actually Fulmer Plant Park, while the Brigadier's home was a private residence called Little Paston. The Doctor's roadster Bessie was seen for the first time since The Five Doctors, with the false licence plate changed from “WHO 1” to “WHO 7”. Shots of Lavel's helicopter were then captured at Black Park in Wexham. On May 7th, material on the grounds of the old farmhouse was filmed at Dowager House in Stamford, Cambridgeshire. On the 8th, the exterior of the Gore Crow Hotel was really Hambleton Old Hall in Hambleton, Leicestershire. Filming should have continued on May 9th and 10th, but this work was cancelled due to a strike caused by a dispute over salaries which pitted the BBC against the Broadcasting and Entertainment Trades Alliance; indeed, rehearsals for Battlefield had already been impacted. As such, work didn't resume until May 11th, when some of the sequences at Warmsly's dig were recorded at Rutland Water in Hambleton.

Next, road scenes were filmed on May 13th and 14th in Twyford Wood near Colsterworth, Lincolnshire. For Ancelyn's arrival, John Nathan-Turner directed a second unit on the 14th, at Castle Cement Quarry in nearby Ketton. May 15th was spent in Hambleton, starting with the war memorial at St Andrew's Church and continuing with additional road sequences. This should have drawn the location work to a close, but the two days lost due to the industrial action had now been rescheduled for May 16th and 17th. Kerrigan's team returned to Rutland Water for the remaining material at the archaeological site.

Cast and crew then spent May 30th to June 1st at BBC Television Centre Studio 3 in White City, London; rehearsals were again hampered by the labour strife involving BETA. In addition to scenes in the farmhouse, Kerrigan also dealt with the TARDIS material on the first day. However, the console room walls had accidentally been destroyed after their appearance in The Greatest Show In The Galaxy the year before. Since Battlefield was the only Season Twenty-Six serial for which it would be required, the production team decided to save money by using a simple set, obscured by dim lighting, rather than construct a long-term replacement. On the middle day, Kerrigan recorded material in the Gore Crow Hotel bar and the UNIT command trailer.

The effect of Mordred's knights bursting into the brewery did not work as intended

The last studio day began with some leftover scenes in the command trailer, for which Aaronovitch asked Cartmel to overhaul the confrontation between the Doctor and Morgaine. Work then continued on the sets for the brewery and the tunnel. The effect of Mordred's knights bursting into the brewery did not work as intended and, with time running short, Nathan-Turner indicated that it should be abandoned; a sound effect would have to suffice. Kerrigan also shot the footage of Morgaine in the crystal ball, before proceeding to the action in the sunken spaceship.

Last of all was the sequence where Ace became trapped in the airlock, which then began filling with water. What no one realised, however, was that the glass used for the tank was not of the appropriate thickness. Once water had been pumped in, with Sophie Aldred hammering on it from the inside, the prop began to lose its structural integrity. Fortunately, as cracks spidered across the glass, Sylvester McCoy realised what was happening and alerted stagehands to the danger. Aldred was pulled clear just as the glass shattered and water poured out over the studio floor. The actress suffered some glass splinters in her hands, but was otherwise unhurt. Nonetheless, tabloid coverage sensationalised the incident, suggesting that Aldred had barely managed to “cheat death”. Footage of the mishap would later be used in BBC safety training videos.

Battlefield was Michael Kerrigan's only Doctor Who assignment, although he would work on spin-off show The Sarah Jane Adventures in 2008. It was thought that Aaronovitch might contribute two serials for Doctor Who's twenty-seventh season; he was also being groomed as a possible successor to Cartmel, having already provided some assistance on the other stories for Season Twenty-Six. However, the cancellation of Doctor Who later in 1989 put paid to all of these plans.

Season Twenty-Six retained the same Wednesday evening timeslot in which Doctor Who had been transmitted the year before, replacing reruns of the sitcom Sorry! starring Ronnie Corbett. Doctor Who would once again follow Wogan, and now led into more repeats, in the form of the crime drama Bergerac. This meant that, for the third year in a row, Doctor Who was tangling with ITV's enormously popular soap opera Coronation Street. Although Season Twenty-Five had witnessed a mild resurgence in the programme's ratings, the premiere of Battlefield Episode One on September 6th was a huge step backwards. With just 3.1 million viewers, it would prove to be the lowest-rated non-repeat broadcast in Doctor Who history. While subsequent installments rebounded slightly, the die had already been cast for the Doctor...

• Doctor Who Magazine #317, “Archive: Battlefield” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who Magazine Special Edition #10, 13th April 2005, “Ride On Time” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #45, 2015, “Story 152: Battlefield”, edited by Mark Wright, Hachette Partworks Ltd.
• Doctor Who: The Eighties by David J Howe, Mark Stammers and Stephen James Walker (1996), Virgin Publishing.
• Doctor Who: The Handbook: The Seventh Doctor by David J Howe and Stephen James Walker (1998), Virgin Publishing.
• In·Vision #101, April 2002, “Production” edited by Anthony Brown, Cybermark Services.