The Doctor and Sarah return to the present day, only to discover that London is all but deserted. Arrested as looters, they are attacked by dinosaurs while being taken to jail. Reunited with UNIT, the Doctor realises that a device is being used to terrorise the city by reaching into the Earth's past. He formulates a plan to track down those responsible -- unaware that Captain Yates is part of the plot, and has been tasked with sabotaging the Doctor's scheme. Meanwhile, Sarah Jane is ambushed while investigating a possible lead. She wakes up to find herself on a spaceship... which left Earth months earlier!

On December 18th, 1972 -- shortly after recording was completed on his Frontier In Space -- Malcolm Hulke submitted a new Doctor Who story idea entitled “Bridgehead From Space”. It concerned the Doctor returning to the present day to discover that aliens had invaded and ordered the evacuation of London, claiming provocation by humanity. A supplicant government remained in the city, in the manner of the Vichy government which nominally ruled France during the Second World War but was, in effect, a puppet regime controlled by Nazi Germany. The aliens planned to demand larger and larger swathes of territory to satisfy their needs; again, this paralleled the events of World War Two, and specifically Adolf Hitler's policy of Lebensraum. Humanity would eventually be limited to Australia, which the aliens then intended to destroy.

At the same time, producer Barry Letts was keen to capitalise on the success of the Drashig puppets employed that year in Carnival Of Monsters, which he felt had established Doctor Who's ability to credibly portray a giant-sized menace. In particular, Letts wanted to set a story during the time of the dinosaurs, which he believed would be enormously popular with children. Letts consulted the BBC's Visual Effects Department, who supported the feasibility of such a project. Script editor Terrance Dicks suggested that the dinosaurs could instead be unleashed in modern times, and it was decided to amend Hulke's narrative to use the giant lizards to terrorise London, rather than aliens.

The production team suggested Mike Yates as one of the people responsible for the dinosaurs

Hulke's revised storyline was commissioned under the title “Timescoop” on January 17th, 1973. The writer was influenced by the tendency to pine for the return of a putative golden age while ignoring its drawbacks. Letts and Dicks suggested that Hulke draw upon the events of the Season Ten finale, The Green Death, in which Mike Yates of the United Nations Intelligence Taskforce (UNIT) was brainwashed by the computer BOSS. Yates would now be positioned as one of the people responsible for the dinosaurs. Dicks thought that Yates might be killed off during the story's events, but Letts felt they might revisit the character in a forthcoming serial.

The scripts for “Timescoop” were commissioned on July 2nd. By this time, Letts and Dicks were heavily involved in post-production on their new, adult-oriented science-fiction series, Moonbase 3, and had agreed to rely strictly on established Doctor Who writers like Hulke for Season Eleven. For the same reason, Letts had to abandon plans to direct “Timescoop” himself, and instead turned to Paddy Russell, whose last Doctor Who work had been on The Massacre Of St Bartholomew's Eve in 1966. Letts felt that Russell would be a good fit for the serial, given her past experience with technically-complex productions; she chose “Timescoop” over the subsequent story, Death To The Daleks. “Timescoop” would be the first adventure made as part of Doctor Who's eleventh recording block but the second in the running order for Season Eleven; it would be preceded by The Time Warrior, which had already been taped at the end of the preceding production block.

By early August, Hulke's serial had been 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. Elisabeth Sladen vexed the production team by cutting her hair short during the summer, contradicting the notion that Invasion Of The Dinosaurs was following on directly from the narrative of The Time Warrior. Sladen would grow her hair back out during the making of the dinosaur serial but this, in turn, would create further continuity issues.

Unusually, Russell's first day of location filming, on September 2nd, was authorised by neither the BBC nor by the relevant government officials. Intent on establishing an appropriately eerie atmosphere for the story, Russell and her camera team posed as tourists and visited several London landmarks early in the morning to capture footage of the “deserted” city. This included Lambeth Pier on the Albert Embankment in Lambeth, Westminster Bridge and the Houses of Parliament in Westminster, Trafalgar Square and the Haymarket in St James's, Margaret Street in Fitzrovia, the Old Billingsgate Market in Billingsgate, the Smithfield Market in Farringdon, and the Covent Garden Market in Covent Garden.

The main filming schedule began on September 23rd, with each day taking in a plethora of London locations. The first day saw the debut of a new vehicle for the Doctor, replacing a scripted motorcycle in Episode Four. This was “The Alien” (referred to in the scripts as the “Whomobile”), a mock-hovercraft which Jon Pertwee had commissioned earlier in the year. He had originally suggested that it be funded by the Doctor Who production office for use in the programme but, when Letts vetoed the idea on the grounds of cost, Pertwee financed it himself and offered it for use on screen anyway. It made its debut in material filmed at the Smithfield Market. Other work on this day included the fight between the tyrannosaur and the apatosaur at the adjacent Lindsay Street in Farringdon, material outside the Underground station at Moorgate Station in Finsbury, and finally the looting of the jewellery store at nearby Phillips Jewellers on Moorfields, with the looter's car crashing on New Union Street.

Work on September 24th began at Northfields Girls' School in West Ealing, which served as the detention centre. The Army land rover could be seen driving along nearby Midhurt Road and Chamberlain Road. The pterodactyl attack took place at Pickford's Depositories in Bowes Park. The 25th was spent in Southall: the looter hid from a passing patrol at the Southall Gas Works, the Army battled the tyrannosaur on The Straight, while the Doctor was pursued by the Army along White Street. Filming for the latter sequence resumed on September 26th at Wimbledon Common in Wimbledon. Russell then spent the rest of the day in Kingston upon Thames: the shuttered police station was really the GPO Sorting Office, the Doctor and Sarah were arrested at the Kingston Meat Market where the Doctor also observed the stegosaur, the milk float was abandoned on Wilmer Close, the Doctor returned to the warehouse via Parkfields Road, and the looters drove past the Doctor and Sarah on Palmer Crescent.

Kingston upon Thames was again the venue for much of September 27th, starting with more of the Doctor and Sarah being detained at the Kingston Meat Market. Next, the TARDIS materialised at Canbury Gardens, the Doctor and Sarah walked to the bus stop along Lower Ham Road, and the Doctor stopped to check readings on South Lane. The Doctor and the Brigadier drove under the apatosaur on Riverside Drive in Ham. The footage of the dog was captured near Burford Road in Brentford. Finally, on September 29th, the Central Electricity Generating Board substation on Elderberry Road in Ealing was the site of the Doctor's attempt to capture the apatosaur, as well as the confrontation with General Finch.

The dinosaurs were far less manoeuvrable and convincing than the Drashigs has been

Model filming took place on October 8th and 9th at an unknown location. Whereas the Drashigs of Carnival Of Monsters had been built by the BBC Visual Effects Department, the unit had ultimately determined that its resources were insufficient to build the dinosaurs required for the model work. Instead, it was suggested that the Doctor Who production team outsource the work to Cliff Culley and his firm, Westbury Design and Optical, who had recently worked on Planet Of The Daleks. However, the dinosaurs exceeded Culley's capacity, and so he subcontracted the models to Rodney Fuller. Letts was very disappointed with the results, which were far less manoeuvrable and convincing than the Drashigs had been. Because the dinosaurs were such an important element of the story, however, their flaws could not be minimised on-screen, leaving Russell and her team to make do with what they had. Fuller's company apparently went out of business soon thereafter.

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 took place on October 15th and 16th at BBC Television Centre Studio 6 in White City, London. The Monday saw the completion of Episode One alongside dinosaur effects shots for Episode Two and the Underground material for Episode Four. The rest of Episode Two was taped on the Tuesday. Several members of the cast and crew were aware that Jon Pertwee was beginning to lose interest in Doctor Who; he still missed Katy Manning, who had played former companion Jo Grant, and had been shaken by the accidental death of Master actor Roger Delgado during the summer.

More model shots were captured on October 18th, 19th and 20th before the second studio session went ahead in TC8 on the 29th and 30th. The Monday was devoted exclusively to Episode Three. On the Tuesday, Russell completed Episode Four, as well as the Episode Six sequence of Sarah's imprisonment in, and subsequent escape from, the store room. This was followed by two final days of model filming, on November 1st and 5th; the latter was held at Pinewood Studios in Iver Heath, Buckinghamshire.

The last studio block for Invasion Of The Dinosaurs took place on November 12th (for Episode Five) and 13th (for Episode Six) in TC4. 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 for Invasion Of The Dinosaurs followed in late November. This was a session involving none of the cast, during which access to the production gallery was permitted while another programme was being set up on the studio floor. It allowed Russell and her team more time to complete the serial's electronic effects, which would have otherwise taken time out of the regular studio days.

Malcolm Hulke was irate at the decision to use the generic title Invasion for Episode One

To preserve the surprise of the monsters' nature, Letts agreed to Russell's suggestion that Episode One be promoted and broadcast as Invasion. Hulke was irate at the use of such a generic title, which he feared would damage the serial's ratings. On January 14th, 1974 -- two days after Episode One aired -- Hulke formally protested a decision he viewed as potentially damaging to his reputation as a writer. Letts subsequently admitted that the gimmick had not only been misguided, but had also been undermined by the advance publicity which unambiguously advertised the dinosaurs' appearance. Both Letts and Head of Serials Ronnie Marsh extended apologies to Hulke; this would turn out to be the writer's last script for Doctor Who.

The BBC Saturday evening schedule changed on February 2nd, the day that Invasion Of The Dinosaurs Episode Four aired. With Bruce Forsyth And The Generation Game having ended its run, Doctor Who now led into the Jimmy Savile programme Clunk-Click, as had been the case for the latter part of Season Ten.

• 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.
• Doctor Who: The Complete History #21, 2017, “Story 71: Invasion Of The Dinosaurs”, 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.