A 2004 advert shows Sullivan Buses RM1069 crossing Parliament Square in the wee small hours as a man wakes up in bed in the foreground. Dean Sullivan comments: “The shot of RM1069 took place early one Sunday morning and required the closure of Parliament Square. The traffic lights were also turned off so as not to distract from the picture.”

To Fly, To Serve
This 2011 advert harking back through the history of passenger aviation (flagged up by Bob Wingrove) is a combination of reconstruction and CGI. We see a red and white single decker, but not clearly:

Youtube 'making of' footage doesn't offer much help identifying this one!

BOAC LYF307D is a 1966 Leyland Atlantean/Metro-Cammell, and it appears twice (distantly) in one scene:

This time it is better seen in the 'making of' footage:

British Airways Sparshatt-bodied halfcab AEC Swift LLH889K makes a brief appearance alongside a Concorde:

….and the 'behind the scenes' footage shows it better: