[clort]

Since you have to book in advance, I guess you give them the number plate details. They can look it up online to see what kind of vehicle it is and can decline to book if too heavy. They can cross check the number plate when you arrive.

[lrae]

TIL you can just look up vehicle information via number plate in the UK.

Possible I guess, but what if you don't have UK plates?

[Symbiote]

That would be rare, they could just decline these bookings.