Hi-tech face scanners are being used at Manchester airport to help stop terrorists and criminals from entering the country, and reduce long queues at immigration checkpoints. The system can be used by those over 18 from the UK and European Economic Area who have biometric passports.
It works by scanning passengers' faces and comparing it to the photograph digitally stored on their passports.
The Lib Dems said the government must ensure the technology is "foolproof".
Facial recognition technology is part of the Home Office's e-Borders programme, which is aimed at transforming the UK's border control to ensure greater security and efficiency.
Ministers believe the facial recognition technology will help identify criminals and terrorists trying to enter the UK illegally.
About 13 million people in the UK have been issued with a biometric passport, which contains a microchip holding biographical information and images.
And a further 30 million people living in the European Economic Area, which incorporates the EU countries plus Iceland, Liechtenstein, Norway, Switzerland, have biometric passports.