Cameras scan the iris's unique pattern

Trusted foreign nationals will be able to volunteer for the scheme which aims to increase security and "revolutionise" immigration controls.

Scans identify volunteers by their unique iris pattern and the government says they are difficult to forge.

Cameras will be used first at Heathrow, then at Stansted, Gatwick, Manchester and Birmingham airports.

The Immigration Service will invite foreign nationals who are permanent UK residents or have work permits to take part and say they will be carefully vetted.

We need to ensure that our controls are robust enough to let in only those with the right to be here Des Browne, immigration minister

In return they are promised faster passage through immigration controls as they will go through special channels equipped with iris-recognition cameras.

Within five years more than one million people are expected to register to use the system, which could be developed for passports and national ID cards.

Immigration Minister Des Browne said the system would give "watertight" confirmation of a passenger's identity.

He said: "More than 90 million people pass through our immigration controls every year.

"We need to ensure that our controls are robust enough to let in only those with the right to be here, and efficient enough to process legitimate passengers quickly."

But concerns have been raised about the ability of biometric technology to cope with exceptional cases - such as someone with very long eyelashes or an eye which is out of focus.

The Home Office has signed a five-year contract with French company Sagem SA to provide the iris-recognition system, but Mr Browne would not reveal the cost on the grounds of "commercial confidentiality".