There were renewed warnings of a summer of travel chaos at British airports yesterday as the Government insisted it would not slow the introduction of passport scanning.

The equipment - designed to read high-tech biometric passports - has already caused long delays at Stansted.

Lin Homer, the chief executive of the Border and Immigration Agency, yesterday said the devices would be installed at all major ports by the end of the year.

The decision has infuriated several airlines, who already face passenger complaints over the security restrictions on outbound passengers' cabin luggage, and fear that extra security checks will mean long delays for incoming passengers.

But Miss Homer played down the threat and insisted that passengers would face only a "slightly longer wait''.

"We have to look at individuals and I make no apology for that,'' she said.

The worst difficulties have been encountered at Stansted, where some passengers have had to wait for over an hour. Last week, Michael O'Leary, the chief executive of Ryanair, criticised the delays.

Within the industry, the greatest fears are the impact the new machinery will have at Heathrow which, according to one industry source, was already on a knife edge.