(BBC comedy series, 2007-24) Episode 1.01
Features Shamrock AIG7914, a 1995 Optare Metrorider:

Seen throughout the three series and returning in the finale is AIG7814, a 1990 Mercedes 814D with Chapmans Travel of Tonyrefail, but seen here with fleetnames for 'Dave's Coaches':

A trip to London has glimpses of a First London Dennis Trident and an Arriva London Sightseeing Leyland Olympian:

(thanks Steve Bunce)

Episode 1.03
Not sure of the location of this Optare Solo, but I'm open to offers as to the owner:

Episode 3.04
Swift but nice footage of Cardiff Bus 193, a Dennis Dart SLF/Plaxton Pointer: