Newer cars are normally serviced by the main dealer who record what the odometer indicates at each occasion it is in the garage, many independents also do this, the SIMI independent non dealer garage that services my car for instance does it, this information is available to car history sites such as Cartell for example, there are others.
NCT picks this up from 4 years of age.
The issue is with imports, if you have the original registration you can search it as well, same thing applies.
Peope need to be more savvy before parting with their hard earned,a car history check is one way, bring along a good car guy another, full car check via AA or other self employed car reviewers is another, they are other ways of course but to succeed the rogue trader must disguise the car being clocked very well, insist on a history, still not satisfied well walk away as there are plenty of other cars available.