Someone suggested maybe to have a dedicated thread for this aspect & I thought it might of interest to some - not sure if it's really needed so mods, feel free to delete if not required:
People can post confirmed examples and I can keep this first post updated with the different allocations for each route involved?
Abellio:
Unidentified double decker(s) - Route U7
Arriva:
ENL21 - Route 325
T36-37 - Route(s) ?
CT Plus:
Enviro 200's of unknown quantity - Route 309
Optare Metrodecker demonstrator YJ16DBO? - unidentified route(s)
Go-Ahead London:
E133-134 - Unidentified BX route(s)
E260 - Route 291
EH81 - Route 37
EN13 - Unidentified garage & route(s)
Ex 8851 & 8864 - Unidentified MG route(s)
SE10 & SE16 - Unidentified SW route(s)
SEN38 - Route 434
Metroline:
VWH2703 & VWH2705 - Route U4
RATP:
DE20030-20031 - Route 413
Stagecoach:
2 Unidentified Optare Solo's - Route 314?
2 Unidentified Optare Solo SR's - Route 261?
8? Unidentified Optare Solo's - Unidentified route(s)
8? Unidentified Optare Solo SR's - Unidentified route(s)
5 363* series Enviro 200's ex Route 323 - Unidentified route(s)
36376 & 36378-36379 - Unidentified route(s)
47632 - Route R7
47641-47642 - Unidentified route(s)
47974 - Unidentified route(s)
48025 & 48033 - Unidentified route(s)
Tower Transit:
Sullivan Buses:
E54-62 - Route 6**
ELV7-9 - Route 6**
TPL926-927 - Route 6**
UNO: