Screenwriter Michael Pertwee was the elder brother of Jon Pertwee, who was enjoying success as the third incarnation of the Doctor in Doctor Who (1963) at the time.
The car and tank chase was clearly filmed around the streets of Borehamwood and Elstree, obviously near to EMI Elstree (Film) Studios. In one shot, in the far background skyline, a tower block can be seen. This is the one close to the nearby ATV Elstree/Borehamwood TV studio complex, that would later become known as Central Independent Television, before the site being sold off to the BBC to become the BBC Elstree complex primarily hosting Eastenders in which the same tower block is sometimes still seen. The then ATV office block known as Neptune House, was also seen in some ATV TV series, as well as in many BBC shows such Grange Hill and Holby City. Its distinctive upper floors are recognisable, in the same background shot in Digby.
Shot at the MGM-EMI Elstree Studios, which were actually the old Associated-British Picture Corporation - the one that was later host to the original Star Wars and Indiana Jones trilogies, before notoriously split in half by late 1980s owners Brent Walker, with one side becoming the Tesco supermarket, and the remaining surviving Elstree (Film) Studios site being bought by Hertsmere Borough Council, and by 2021 hosting various TV and films such as Paddington, Strictly Come Dancing, and The Crown.
The Good Companion's Cafe scene was filmed on the B556 St. Albans Road in South Mimms, Hertfordshire. The Cafe has since been demolished but Arlingham House seen next door and the car park still remains.