Before I was a bus driver I did eight years airside at Glasgow as a load controller; our airside buses were a couple of DAFs (H104 VUB & R987 FNW) and four Dennis Lances (L21/3 AUS, M726 HHS, K740 YPJ), as was mentioned Edinburgh had some Pointer Darts - M882-4 XSC and N301 HSC from memory.
"Proper" airside buses are generally built to a 3m width and are very difficult, if not impossible to road register as they don't really meet C&U regs.
Generally speaking most of our airside kit was pretty done but a lot of it had been road registered in the past if it wasn't too specialised; it wasn't uncommon for rebodying to happen, where stuff like Air Start Units were mounted on multiple chassis as they tended to last pretty long and were expensive to replace. British Airways registered almost everything until well into the 1990s, ULD loaders, cargo kings, electric tugs, pushback tractors, the lot; I went to the chippy in a Douglas DC10H registered C608 XLF, before it was rapidly deregistered and replated as AV02 212 🤣
We tended to replace the road registrations with fleet number plates when vehicles went airside only, Servisair tended to remove every trace of ID and just number them - this was a requirement for Airside Operations for ID purposes; the same Volvo FL6.17 in three photos here, G635 VMM at Gatwick in Midland livery, then as AV01 635 with aviance, then 29-3744 with Servisair.
@Urkoas an aside, no matter what chassis it actually was, any flatbed baggage lorry in our place - Transits, LDVs, EuroCargos, Ford Cargos, DAF 45s, anything at all - was always referred to as a bantam. It was the end of 2010 when I left...