(11 Jan 2024, 6:08 pm)busmanT wrote Driver training buses have to be a minimum of 10 metres long and capable of a minimum of 50 mph by law.
Obviously GNE have chosen to go with single deckers as that's what they chose was best, focusing on the extra metre or so, but the B9's are 10.4m in length at least.
Arriva have double decker trainers in the North East, nevermind in London where it's all they have pretty much.
https://cptdb.ca/wiki/index.php/Go-Ahead_London - The lengths are on there.