The underground nuclear bunker broken into by Messrs Griffin and McAndrew is the actual site that would have housed Britain's government in the event of nuclear war. It is situated in Essex, between the towns of Brentwood and Ongar. The break-in was unnecessary, however; the bunker is open to the public.
There are at least two references to the film Threads (1984) which is about a nuclear attack on a city in the UK.
First of all, William Taskerland says he was at a conference in Sheffield which is where Threads is set and filmed.
Secondly, Carla O'Brien lives on Dinsdale Close. Reece Dinsdale stars in Threads.
There was a War Game in Europe in 1983 but it was called Operation Able Archer, not Zachariah but the effects were the same, the USSR readied for war and Europe came close to being wiped off the map
A key scene in UCOS saw the characters watching footage from the UK Government's infamous public information campaign Protect and Survive (1976)