Here's footage of the Hood/Roe Street Gyratory known locally as the 'Bubbles' in Liverpool from the mid 70's.
The video says 1970 but it's most likely '77 or "78 that was shot judging from bus liveries and street scene and the fact the Gyratory wasn't finished until 1976. It was all part of the St John's Shopping Centre redevelopment (which arguably wasn't as good as what it replaced) and a move to bring urban motorways to central Liverpool which weren't built in the end and would have smashed through much of the city's Georgian Quarter which features in many period drama's these days too, hence why the M62 suddenly ends at the Rocket Roundabout.
Hood/Roe Street Gyratory wasn't a nice place with either a dangerous cross of 4-5 lanes of traffic or risk the walkway's (streets in the sky) which ultimately became magnets for vandalism, crime and ASB. Traffic lights were added in the mid '80's and one of the walkway's demolished in '92 and by 1995 a decision to completely redevelop the area under it's original name of Queen Square was taken which was completed by 1996-98. Not necessarily perfect Queen Square is a massive improvement over what was there before and here's a contemporary view of the area below.
I would tend to agree that it's early 80s, probably 80/81. I saw what looked to be a Mark 5 Cortina at the start, which came out in September 79, and it looked to be earlier in the year than Autumn.