UNIT is called to a nuclear reactor on Wenley Moor, which has been plagued by strange power disruptions and a wave of nervous breakdowns. The Doctor suspects a connection with a nearby network of caves, and is stunned to find a dinosaur hunting in the tunnels. He discovers that the reactor has inadvertently awakened the Earth's original inhabitants: the reptilian Silurians, who have lain underground in suspended animation for millions of years. Now the Doctor must determine whether there is any possibility for peace between the two races -- or whether a catastrophic conflict is inevitable.

By the spring of 1969, Doctor Who's seventh season had been given the green light by the BBC. It would adopt a new format devised by producers Peter Bryant and Derrick Sherwin, in which the Doctor was trapped on Earth and working with the United Nations Intelligence Taskforce (UNIT). Attention now turned to finding suitable scripts which would reflect the programme's revamped status quo. Amongst those approached by script editor Terrance Dicks was Malcolm Hulke, who had never previously written for Doctor Who solo, but had collaborated with David Ellis on 1967's The Faceless Ones and with Dicks himself on the Season Six finale, The War Games. Hulke was initially reticent, voicing the opinion that the Earthbound setting restricted the programme to adventures involving either alien invasions or mad scientists. However, he agreed to try to prove himself wrong.

To this end, Hulke developed a narrative about a race of creatures which would be revealed as having inhabited the Earth millions of years before mankind. On June 15th, Dicks commissioned a six-part serial from Hulke called “The Monsters”. Hulke and Dicks explored the terminology given to the Earth's various geologic eras, and settled on naming the story's creatures after the Silurian period. Spanning twenty-five million years and occurring a little more than four hundred million years ago, it was during the Silurian period that the first bony fish appeared, but terrestrial animal life still only consisted of small creatures like arthropods. As such, it was not truly appropriate to the sophisticated reptilian bipeds which Hulke envisaged, but he and Dicks felt that “Silurian” sounded appropriately spooky. The scripts were therefore commissioned under the title The Silurians on August 11th; the serial was expanded to a seventh episode at the same time.

The Silurians' third eye was suggested by director Timothy Combe

To this point, Hulke's adventure was intended to be made and aired third in Season Seven, coming after David Whitaker's The Ambassadors Of Death. When that story hit severe scripting difficulties, however, Dicks elected to transpose the two in the running order, moving The Silurians up to second. Minor alterations made to Hulke's scripts included promoting Hawkins from Sergeant to Captain, and the removal of dialogue which explained that Quinn had always wanted to be a geologist but had been pressured into studying physics by his father, a pioneer of the atomic field. The Silurians' third eye was suggested by the assigned director, Timothy Combe. Combe had previous experience with Doctor Who, having been an assistant floor manager on The Keys Of Marinus and a production assistant on both The Reign Of Terror and The Evil Of The Daleks.

Meanwhile, major changes were afoot in the Doctor Who production office. Bryant and Sherwin had essentially been sharing the producer's duties in recent months and, although Sherwin had been credited as such on the two preceding serials, it appears that Bryant was intended to be the listed producer on The Silurians. But, in October, both Bryant and Sherwin were reassigned to a problematic mystery series called Paul Temple, and Barry Letts was named Doctor Who's new producer. However, Letts still had commitments to the soap opera The Doctors which would prevent him from taking an active role in the pre-production of The Silurians. These duties instead fell to assistant script editor Trevor Ray, who would thereafter join Bryant and Sherwin on Paul Temple.

Production on The Silurians began a week late, due to the same industrial action by the Association of Broadcast Staff which had forced the season premiere, Spearhead From Space, to be recorded entirely on film. As a result, John Newman was hired to play Spencer in place of Bernard Finch, who had originally been cast in the role but was not available for the revised dates. Filming began on November 12th in London for the Episode Six sequence in which the infected Masters arrives in the city. He disembarked the train at Marylebone Station, exited his taxi at the nearby corner of Dorset Square and Balcombe Street, and then staggered along Edward Woods Estate in Notting Hill.

November 13th and 14th were spent at Sheephatch Farm in Tilford, Surrey, which served as Squire's farm. Publicity shots were also taken of Bessie, the Doctor's new car, which would debut in The Silurians. The element of the Doctor borrowing a vintage automobile had appeared in the script for Spearhead From Space, and both Jon Pertwee and Trevor Ray had suggested to Peter Bryant that it might become a permanent fixture. Bryant felt that giving the Doctor a distinctive vehicle would help replace the TARDIS, which would now have a more minor role in Doctor Who under the new format. Work on Bessie was under way from August, and the car was built on a Ford Popular chassis by Glentura Plastics in the style of an Edwardian roadster. Bessie bore a fake license plate reading WHO1 although, since this plate number was already registered, its actual plate was the more mundane MTR5. Letts was subsequently unhappy with the jokey nature of the plate number.

Cast and crew remained in Surrey for the following week. The first venue was Hankley Common in Rushmoor, which posed as Wenley Moor on November 17th and 18th. Wenley Hospital was actually Milford Chest Hospital in Milford; scenes there were filmed on the 19th. Work on November 20th started in Godalming, where Bessie drove down the high street. Next, the Hog's Back Transmitter Station in Guildford served as the exterior of the research centre, and was also used for the sequence where the Doctor watched UNIT blow up the Silurian caves. The latter was apparently added to the narrative by Dicks at Letts' request. The new producer had discovered from audience research reports that over half of Doctor Who's viewers were adults, and he therefore sought to orient the programme in a more mature direction. Unfortunately, the filming of the explosion did not go as planned and a small grass fire was ignited, forcing Ray to explain the mishap to the local firefighters.

Although this should have concluded filming for The Silurians, Letts felt that Combe had captured an insufficient number of close-ups for the plague material filmed at Marylebone Station. As such, a remount was secured by claiming -- falsely -- that the processing lab had accidentally destroyed the footage. Combe returned to Marylebone on November 24th; several members of the production staff made cameo appearances, including Ray as the ticket collector, and Letts and Dicks as passengers.

The advent of colour recording meant that the chroma key technique was now available for Doctor Who

One element of The Silurians that proved unexpectedly problematic was the caves. Combe had originally contemplated filming at least some of this material at Wookey Hole in Somerset. However, it became clear that this would not be logistically feasible, and so Combe elected to move these sequences into the studio. It was next suggested that they could be recorded by inserting actors onto model sets. The advent of colour broadcasting meant that the chroma key technique -- which the BBC referred to as colour separation overlay, and which had been in use, in various forms, on movies for a number of years -- was now available for television programmes. Chroma key involved one camera recording action which played out against a uniformly-coloured background -- typically either a blue, yellow or green screen -- with this “key” colour then electronically replaced with images which had been pre-recorded or were being captured by a second camera. However, at this stage, the technology was sufficiently primitive that a visible fringe of colour often surrounded the actors, and so its use to the extent that Combe envisaged was deemed impractical.

Finally, it was decided that the caves would simply be represented by regular sets. Because the BBC did not have the equipment that designer Barry Newbery needed for construction, he instead hired outside contractors to perform the work. When Newbery went to collect the finished sets, he was horrified to discover that the company had not built a framework on which to mount the walls -- and, despite the firm's assurances, the sets were indeed too flimsy to stand erect. As a result, it was decided to abandon Doctor Who's usual production pattern, in which each week's studio session was devoted to a single episode. In recent years, improvements in editing technology had increasingly facilitated out-of-sequence recording, and now all of the cave scenes would be made together during the second studio date, on December 15th. This would provide Newbery with the time to assemble a new cave set, for which he principally used stock elements, together with some hastily-constructed stalagmites and stalactites.

Consequently, the first studio session involved the recording of all the material for Episode One not set in the caves. This work took place on Monday, December 8th at BBC Television Centre Studio 3 in White City, London. It was a week later, on the 15th, that cave scenes from a variety of episodes were taped in TC1. A large dinosaur costume, inhabited by an actor, was constructed for these sequences. However, because it had to be enlarged using chroma key in some shots, Combe belatedly realised that it would have been both cheaper and more effective to simply build a small model dinosaur. Also recorded on the 15th were some of the opening credit sequences. Unfortunately, in a break with tradition, the story's title was given as “Doctor Who and the Silurians”. Although this was the style used on most Doctor Who scripts to date, the “Doctor Who and...” prefix had always been omitted from the title given on-screen. To avoid a recurrence of this error in the future, the prefix was largely dropped from subsequent scripts.

Barry Letts felt that taping two episodes together on a biweekly basis would be a more efficient approach

Another innovation occurred the following week, which saw Doctor Who in TC1 on both Sunday, December 21st and Monday, December 22nd. Time had run out to complete the cave scenes scheduled for the 15th, and so an extra day of work was scheduled for the Sunday. Letts also felt that taping two episodes together on a biweekly basis would be a more efficient approach than the traditional scheme of recording one episode each week. In particular, since major sets could be left up overnight, the number of times they would be struck would be cut in half, thereby reducing the amount of damage they incurred. The 22nd saw the completion of all the remaining scenes for Episodes Two and Three. Also recorded on this day was the Episode Four material set in Quinn's cottage, to avoid the need to erect the set again at a later date.

Cast and crew then broke for the Christmas holidays, with recording resuming on January 5th, 1970. The remaining four studio sessions were more traditional in nature, with a single episode taped on consecutive Mondays. The venue for Episodes Four and Five remained TC1, while Episodes Six and Seven moved to TC8. The Silurians was completed on January 26th.

• Doctor Who Magazine #222, 15th February 1995, “Archive: Doctor Who and The Silurians” by Andrew Pixley, Marvel Comics UK Ltd.
• Doctor Who Magazine Special Edition #2, 5th September 2002, “Instant Karma” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #15, 2016, “Story 52: Doctor Who and The Silurians”, edited by John Ainsworth, Hachette Partworks Ltd.
• Doctor Who: The Handbook: The Third Doctor by David J Howe and Stephen James Walker (1996), Virgin Publishing.
• Doctor Who: The Seventies by David J Howe, Mark Stammers and Stephen James Walker (1994), Virgin Publishing.