There are at least 3 different shots of RT/RTL/RTW class buses with circus (and of course film pre-release) 'See Gorgo' ads on the sides - the first shot looks to be in an LT garage with 3 buses pulling out in succession, then general handheld shots in the streets of London ending with one being filmed racing through Trafalgar Square. Three others (the same three?) feature at the climax of the film (static) as Gorgo devastates Central London.
Also many model shots as Gorgo trashes Picadilly Circus and one reversed shot showing an RT-type advertising "XULUD" paint withan OFFSIDE staircase. Two brief shots also show a maroon/whiteutility looking double decker in the background near the end - most certainly not LT liveried!" (thanks Scot Fergie) The front two of the LT garage sequence are RTLs for route 88, the middle one is RTL741 (KXW91). This is apparently Stockwell garage, since the buses all have SW garage plates:
