(1992-2010)
Episode 1.2:
United Automobile Leyland-National 2 3117 (APT117W) appears; there's a certain amount of condensation on the windows inside. (thanks Mark Harrington and Mike Lloyd)
There's also the fleetingest of glimpses of a Yorkshire Rider double decker through a car window:
Episode 4.1:
Ex-London Transport AEC Routemaster RM1414 (414CLT) is in a scene set in Reading; vehicle supplied by the Museum of Transport, Manchester (thanks Bob Wingrove)
“A Touch of Frost is filmed in the Yorkshire TV area which is why there are only rarely sightings of buses on it since it is set in the Thames Valley area. In a very early episode Frost was seen entering a house as a Yorkshire Rider Metrobus passed by going to Leeds Central Bus Station!” (thanks Chris Hough)
Episode 4.4:
“A West Riding Leyland Lynx 2 (in Caldaire Green livery) is seen through the rear windscreen of Jack Frost's car as he passes it as it pulls up at a bus stop.” (thanks Paul Bennett)
Episode 13.2:
Rob Sissons notes “a man is freed from prison and is seen travelling on Greater Manchester South 859 (P859GND, Volvo B10M-55/Alexander).” This is now Stagecoach Manchester 20859; the original fleetnames have been covered with fictitious 'Arrobus' logos. Although there's no fleet number visible on the front of the bus, it can be seen at the rear offside in the third screenshot.
Episode 13.3:
Rob Sissons drew my attention to the Optare Spectra in this episode, but when I investigated further I found more buses of interest. Initially Arriva Yorkshire 470 (S470GUB), a DAF SB220/Alexander, is the scene of an altercation that ends with the driver being stabbed in the hand. In the third screenshot it's pulling into a bus station.
Back at the 'Arrobus' garage we see a number of different Arriva Yorkshire vehicles, a step entrance Dennis Dart/Plaxton first, then a low floor Dennis Dart MPD/Plaxton, 212 (V212PCX)
Next to it is a step entrance DAF/Optare Spectra, and then a low floor Dennis Dart/Plaxton:
Rob Sissons notes this episode “features an attack on a bus crew and includes a shot of Arriva Yorkshire 706 (YG52CFE), a low floor DAF/Optare Spectra. Again, the original fleetnames have been covered with fictitious 'Arrobus' logos.”
Paul Bennett identifies the garage: “The Depot is Arriva Yorkshire Belle Isle (Wakefield) Depot. The bus station was used for filming one Sunday morning and stands 1 to 5 were used. We had to use other stands in the bus station whilst filming was ongoing. The Depot was used for filming earlier in the same week. I remember they were filming in the cashing-in room one lunch time when I had just finished my shift. I was stood about 10 feet away from David Jason!”