They do check the mileage at the MOT. If you go to the MOT check website www.check-mot.service.gov.uk you can get the MOT history of any car and see the mileage recorded at the time of the test.

I'd suggest that the biggest issue is with cars up to 3 years old, to avoid excess mileage charges on PCPs and leases - so too late to start checking once an MoT is needed.

In the first 3 years of ownership, no one can really tell if a car has done 20,000 or 80,000 miles.

If a car has done 80K miles it should have had at least 4 services. If there is no evidence to show that, best left alone. If it has done 20K in 3 years, likewise - if there is no service history, best left alone. Most cars of that age reappear from dealers, and if they or the previous owner (or lessor) can't be bothered to keep useful documents, that car loses some resale value.

If the OP is suggesting that cars should have MoT checks from year 1 to validate mileage, a nice idea, but I can't see it catching on.

I believe that BMWs update the mileage on the key each time it is used. Years ago, when taking my car in for a service, they just read the mileage from the key.

In these days of much more connected vehicles, it should be simple to update a central record each time the car is used. I'm sure some will complain on privacy grounds, but it seems sensible to me.

Pointless doing a yearly 'mileage MOT' as those that clock them would, I imagine, time the clocking before the mileage check, just like they time it before services and normal MOT's.

I don't believe the mileage of any car unless I've had it from new, or know and trust the person who has.

The answer is to physically and technologically make it as hard as possible to tamper with the car's mileage, and make it illegal to do so.