The ban on taking more than one piece of hand luggage on board aircraft will be lifted, government officials said yesterday, but not until after the summer holidays.

Millions of families heading abroad can expect frustrating delays of up to an hour queueing at security check-points as the big holiday rush begins over the next few weeks. The Department for Transport told aviation industry leaders at a special meeting on security that it would not be altering any of its stringent rules because of security fears.

Restrictions on hand luggage were imposed last August after an alleged plot was uncovered to blow up transatlantic airliners.

The rest of Europe, the US and Australia have followed Britain in placing restrictions on liquids in hand luggage but no other country limits its passengers to one carry-on bag. Officials are understood to be preparing to allow passengers to take bags on board but they have decided to wait until the autumn.

Meanwhile, BA admitted for the first time that it was having to send thousands of bags to Milan by lorry for processing after failing to load them on to aircraft with their owners. A BA spokesman said that its Heathrow processing centre lacked the capacity to cope with all the extra bags that were being checked in.

BAA, which owns Heathrow, Gatwick and Stansted, said that it had recruited 1,400 additional security staff since last August, a 30 per cent increase. A BAA spokesman said: “There is no ceiling on the number of security staff we will have. We just keep recruiting as fast as we can but they take 15 weeks to vet and train.”

He denied that the resignation, announced yesterday, of Tony Douglas, Heathrow’s chief executive, would undermine efforts to reduce security delays at the airport.

To ease the situation a five-week trial began at Heathrow on Monday in which passengers transferring between flights are being allowed two items of hand luggage. Passengers will continue indefinitely to be banned from carrying through security checks any liquid containers with a capacity of more than 100ml, which is about the size of a tube of toothpaste.

Airlines are now concerned that the delays will only be lengthened as staff struggle to explain the rules to thousands of people who have not flown since last summer. London First, the business lobby group, has written to the DfT complaining that no groups representing passengers were allowed to attend yesterday’s security meeting.

The industry agreed yesterday to set up a working group that will hold regular meetings with officials on security issues, including the need to provide evidence that the one-bag rule could be lifted safely.

Ruth Kelly, the Transport Secretary, who attended yesterday's meeting, said: “We will not compromise on the safety of passengers, and this means that the heightened security measures introduced last summer are still necessary. But I am only too aware that as the main summer season approaches, better preparations need to be put in place. We are running a campaign to help ensure passengers arrive prepared for the current luggage arrangements, and we have made changes where possible to help make the security process quicker.

“In time we are willing to make further changes, for instance on the one-bag rule. But currently the ball is in the industry’s court. ”

Speaking after leaving the meeting, Willie Walsh, chief executive of British Airways, said: “I made it very clear that the one piece of hand luggage restriction which applies to customers departing the UK and transferring through the UK has no security justification and has become intensely irritating to customers.

“The restriction is also damaging the UK’s reputation around the world from a business perspective.”

Ryanair complained to the DfT yesterday about not being invited to the meeting with Ms Kelly, despite carrying more passengers than BA.