https://www.gov.uk/check-mot-history
Throw in the reg there and it'll give you an insight on the MOT's it shows each mileage value at every MOT. Bear in mind the first 3 years do not need a MOT so take a look at the first MOT and see the value there.
Many people will do 60k, clock back to 20k before the first MOT and not touch it after that to keep it a clean history, Try and do as much research on the car before you buy it and always as i've always said if its too good to be true it most likely is. However many times in my life that phrase has been completely proved wrong and i've found some gems.
-Regards Matti