> Maximum weight: 2.6 tonnes

Wonder what the actual limit is and what happens when you're above it (and the other max. dimensions)? Couple of EVs out there that are heavier than 2.6 tonnes now. (Volvo EX90, Mercedes EQS, BMW iX, Ioniq 9, Rivians (not yet in the UK), ... and many more right around that weight.)

Is it getting measured in the cabin and declines you?

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.