From 30 November 2009, the UK Border Agency is introducing fingerprint checks at the border for passengers with biometric UK visas and entry clearances.

On arrival in the UK, passengers with biometric UK visas and entry clearances will have their fingerprints scanned at border control. In the majority of cases the passenger’s right hand thumb and first finger will be used. These will then be checked against the fingerprints provided in the application process.

According to UK Border Agency:

The purpose of this check is to verify that the individual entering the UK is the same person who applied for their visa / entry clearance and using fingerprints enables us to do this with greater certainty.

UK Border Agency has a frequently asked questions list on their website.