Passengers flying into Gatwick Airport from Sierra Leone with biometric visas are having their fingerprints recorded in a pilot scheme.
The BioDev trial aims to flush out false visa applications and strengthen border security at the airport.
Travellers have digital photographs and fingerprints checked, and anyone found attempting to come into the UK illegally will be refused entry.
The workings of the trial were seen by Immigration Minister Liam Byrne.
Mr Byrne said: "New fingerprint visas are fast becoming our first line of defence against illegal immigration.
"By establishing people's identities beyond any doubt before they enter the UK, we can stamp out multiple applications and identity fraud - ensuring entry only to those who are welcome."
The first phase of the project is due to finish in April 2008.