U - UK-sourced/UK specification
UK-sourced/UK specification/UK spec - It's crucial to understand the difference between a car which is UK-sourced and one which is to UK specification.
The former is a car which has been ordered and supplied by a UK franchised dealer. If you read the latter in an advert, however, the likelihood is that the car has been imported. It may not be important at the time but, in the worst case, it could seriously affect the value of the car at trade-in time.
As a rule, always make sure an import is to full UK specification. If you are buying a car which is not to UK specification, haggle a decent discount.