LONDON, England - April 5, 2009 - In a leaked memo, an official says that airport face scanning machines have been recalibrated to an "unacceptable" level, meaning travellers whose faces are shown to have only a 30 per cent likeness to their passport photographs can pass through security.

The machines, undergoing trials at Manchester Airport, have apparently been questioning so many passengers' identities that they were creating huge queues.

The technology was designed to help immigration officials spot people traveling under false passports, particularly terrorists, but the multi-million pound scheme now appears to be in jeopardy.

In the email, the official says: "Update on the calibration - the facial recognition booths are letting passengers through at 30%.

"Changes appear to have been made without any explanation [or] giving anyone a reason for the machines [creating] what is in effect a 70% error rate.

"[The fact that] the machines do not operate at 100% is unacceptable. In addition it would be interesting to know why the acceptance level has been allowed to decrease."

Rob Jenkins, an expert in facial recognition at Glasgow University's psychology department, said lowering the match level to 30 per cent would make the system almost worthless.

Using facial recognition software from Sydney airport in Australia set at 30 per cent, he found the machines could not tell the difference between Osama bin Laden and the actors Kevin Spacey or even the actress Winona Ryder while Gordon Brown was indistinguishable from Mel Gibson.