To dispel a further myth, a Dart (picture 4) is not a full sized bus, but a midi bus!
I am advised there are two types of Darts - regular ones and longer ones. I don't know which one's pictured here, but I understand that both lengths have been in use on the Rail Replacement service.
Its better than that
They are available in
8.5m, 8.8m, 9.0m, 9.2m, 9.3m, 9.8m,10.0m, 10.1m, 10.6m, 10.7m, 11.3m
At least 10 different body styles,
A narrow bodied version specifically for the Channel Islands!
No Dart body style or Length is deemed "full size" in the industry.
Full size would refer to something like the Volvo B7RLE or B10M, which from the photo of the Dart would fit in easily as you're only talking a metre or so longer and fractionally wider