When the Doctor and Sarah Jane return to modern-day England, they find London deserted and dinosaurs on the loose. It transpires that a group of politicians and scientists are trying to right what they perceive as the cause of all our planet's wrongs by reverting the Earth to a pre-technological level. To make matters worse, they have help -- from inside UNIT and amongst the Doctor's closest friends.

On December 18th, 1972 -- shortly after recording was completed on his Frontier In Space -- Malcolm Hulke submitted a new story idea entitled “Bridgehead From Space” to the Doctor Who production office. This concerned the Doctor returning to the present day to discover that aliens have invaded and ordered the evacuation of London, claiming provocation by humanity. The aliens plan to eventually convince mankind to cede to them all lands except for Australia (in the manner of Hitler's tactics prior to World War II), which they will then destroy.

At the same time, producer Barry Letts was keen to capitalise on the success of the Drashig puppets employed in Carnival Of Monsters. In particular, he thought that Doctor Who could attempt a story set during the time of the dinosaurs, drawing on the enormous popularity of the giant lizards with children. Letts conferred with the Visual Effects department, who confirmed that this would be within their capabilities. Script editor Terrance Dicks suggested that the dinosaurs could instead be unleashed in modern times, and it was decided that Hulke's storyline would be amended to have London terrorised by dinosaurs instead of aliens. Letts and Dicks also suggested that Hulke draw upon Mike Yates' betrayal of UNIT (under the influence of the computer BOSS) in The Green Death, and have him be one of the people responsible for the dinosaurs.

Hulke's revised storyline was commissioned under the title “Timescoop” on January 17th, 1973; the request for scripts came on July 2nd. Shortly afterward, Serial WWW was retitled Invasion Of The Dinosaurs. Richard Franklin was booked to play Yates on September 5th, while Nicholas Courtney's services as Brigadier Lethbridge Stewart were secured on the 14th.

Despite being planned as the second story of Season Eleven, Invasion Of The Dinosaurs was the first to be made as part of Doctor Who's eleventh recording block (The Time Warrior having been taped at the end of the tenth block). It was also the second serial in a row which Letts found himself wanting, but unable, to direct because of his responsibilities to the adult science-fiction series Moonbase 3. Instead, the director's chair was assigned to Paddy Russell, whose last Doctor Who work had been The Massacre Of St Bartholomew's Eve seven years earlier.

Unusually, Russell's first day of location filming, on September 2nd, was unauthorised by the BBC or by the relevant officials. Intent on establishing an appropriate atmosphere for the story, Russell and her camera team -- posing as tourists -- visited several London landmarks early in the morning to capture footage of the “deserted” city. The main filming schedule spanned the 23rd to the 27th, plus the 29th, and took in a plethora of London locations.

The 23rd saw the debut of a new vehicle for the Doctor, replacing what Hulke had originally written as a motorcycle in episode four. This was “The Alien” (referred to in the scripts as the “Whomobile”), a mock-hovercraft which Jon Pertwee had had built earlier in the year. He had originally suggested its fabrication to Letts, but when the producer vetoed the idea on the grounds of cost, Pertwee financed it himself.

Two days for model filming then occurred on October 8th and 9th before recording moved to the studio. As with most of the previous year, the studio schedule for Invasion Of The Dinosaurs was divided into fortnightly two-day sessions, taking place on Mondays and Tuesdays. The first of these transpired on the 15th and 16th in BBC Television Centre Studio 6. This concerned material for parts one and two, plus the Underground segments for the fourth installment. By now, unfortunately, it was clear that the dinosaur puppets -- the construction of which had been contracted out to an external firm due to the size of the models -- were far less convincing than the production team had anticipated. Because the dinosaurs were such an important element of the story, however, these flaws could not be minimised onscreen, leaving Russell and her team to make do with what they had.

More model shots were captured on the 18th, 19th and 20th before the second studio session went ahead in TC8 on the 29th and 30th. This involved the completion of episodes three and four, as well as the part six sequence of Sarah Jane's imprisonment in, and escape from, the store room. This was followed by two further days of model filming, on November 1st and 6th.

The last studio block occurred on November 12th and 13th in TC4, finishing all the outstanding material from the fifth and sixth installments. George Bryson, who had been cast as Private Ogden, proved unavailable for these dates and so the character was replaced with Private Bryson (unflatteringly described as “rather dim” in the revised scripts), played by Colin Bell. For the first time in Doctor Who's history, a “gallery only” day followed in late November. This was a session involving none of the cast, allowing Russell and her team to assemble the serial and complete work on electronic effects.

Letts latterly decided to keep the identity of the serial's monsters a secret by airing the first episode under the truncated title Invasion. This met with displeasure from Hulke, who thought that the abrupt change of moniker with episode two, combined with the possible loss of ratings due to the boring and generic title, was injurious to his reputation. It was also an unsuccessful gambit, because considerable advance publicity advertised the dinosaurs' appearance anyway. (The move also lead to one of the most widely-believed myths in Doctor Who folklore, with fans later believing that the reason behind the destruction of only the print of the first episode of Invasion Of The Dinosaurs was because it had been erroneously identified as part of the Patrick Troughton story The Invasion.) Letts subsequently apologised to Hulke, as did Head of Serials Ronnie Marsh.

Invasion Of The Dinosaurs would transpire to be Hulke's final Doctor Who serial. Having tired somewhat of writing for the televised programme, he found more joy in writing novelisations for Target's Doctor Who range. In April 1979, Hulke fell ill and, after suffering a relapse, died peacefully in hospital on July 6th of that year.

• Doctor Who: The Handbook: The Third Doctor by David J Howe and Stephen James Walker (1996), Virgin Publishing, ISBN 0 426 20486 7.
• Doctor Who: The Seventies by David J Howe, Mark Stammers and Stephen James Walker (1994), Virgin Publishing, ISBN 1 85227 444 1.
• Doctor Who Magazine #203, 1st September 1993, “Archive: Invasion Of The Dinosaurs” by Andrew Pixley, Marvel Comics UK Ltd.
• Doctor Who Magazine Special Edition #2, 5th September 2002, “The Show Must Go On” by Andrew Pixley, Panini Publishing Ltd.