Air passengers are being warned by airport operator BAA to expect peak-time delays at major UK airports for the rest of the year.
BAA, whose seven UK airports include Heathrow, Gatwick and Stansted, has issued the stark warning despite plans to recruit more security staff and open more security lanes.
BAA chief executive Stephen Nelson said it wants to eventually reduce queuing at airports to five minutes or less for 95% of the time but added that this figure could not be guaranteed immediately.
At a media dinner in London he said: "We will not be able to guarantee it - not at Easter, not even in the summer.
"You say is this the end of marquees (for waiting passengers) coming up to Christmas? We can't guarantee that right now."
Mr Nelson said it was hoped the five-minute target would be met outside peak times at Heathrow this summer and that the target would be close to being achieved at Gatwick and Edinburgh during the summer.
He said that Stansted was more of a "long-term story" and that there were problems to overcome at Aberdeen and Glasgow airports, while Southampton had "pretty much" reached the target already.
Mr Nelson was speaking as BAA announced that it was spending £40 million to recruit 1,400 security staff and open 22 new security lanes at its seven UK airports.
Mr Nelson said that his company was offering "an unacceptable delivery for too many passengers in terms of queues".
He said there were problems with lifts, escalators, travellators and toilets, some of which were not up to standard.
He also warned that there were physical constraints at Glasgow airport, in parts of Stansted and at Heathrow's Terminal 2 which meant the delivery of the five-minute target was not possible.
Mr Nelson said that an end to congestion was possible at BAA's airports but he added that the company "has a long way to go from the current position".
Heathrow chief executive Tony Douglas said: "There is no question that customer service at Heathrow has been unacceptable and at times it continues to be unacceptable."
He said that Heathrow had already taken on 500 more security staff, recruited from 9,000 applicants, but admitted that that in terms of cleanliness, Heathrow had "challenges".
Mr Douglas said that it was hoped that the Heathrow East development, serving 30 million passengers a year in a new terminal to replace the existing Terminal 2, would be ready by June 2012 - the month before the London Olympics.
Their comments came ahead of two imminent referrals to the Competition Commission of matters relating to BAA.
The Office of Fair Trading (OFT) is likely to make a reference to the commission about airport ownership.
In December 2006, the OFT said it suspected that the BAA ownership of airports, the system of economic regulation of airports and capacity constraints combined to prevent, restrict or distort competition.
On Friday, the Civil Aviation Authority is due to send the Competition Commission its proposal for how much BAA can charge airlines to use Heathrow and Gatwick.
The proposals could see BAA forced to reduce its current charges in time for 2008-13.
Mr Nelson said that as well as tackling congestion at the airports, BAA was ready to make major, long-term investments in British airports and that the onus was on the regulatory authorities to "deliver the stable regulatory system and sensible financial incentives necessary to deliver these plans".
