The operator of Heathrow, Gatwick and Stansted airports has warned that passengers must expect slow check-in times in peak periods to continue.
Passengers have probably not seen the end of long waits, BAA says.
BAA wants to cut queue waiting to five minutes, 95% of the time.
But it said that the target could not be guaranteed by Easter or summer and did not rule out using marquees for waiting passengers outside terminals.
The boss of Heathrow Airport has also admitted that customer service there was "unacceptable" at times.
BAA, which is also the operator of Aberdeen, Edinburgh, Glasgow and Southampton, is to spend £40m recruiting 1,400 security staff and opening 22 security lanes at its UK airports.
Chief executive Stephen Nelson said that this would improve service in the long term, but that it would take time to reach its targets.
Currently, his company was offering "an unacceptable delivery for too many passengers in terms of queues", Mr Nelson said.
Over the past year BAA has faced a string of problems.
It came under fire for how it handled heightened security measures introduced after August's bomb alert.
And over the Christmas period, fog brought chaos to Heathrow, leaving thousands of passengers stranded.
This led to white marquees being erected outside terminals to act as temporary holding areas to ease the pressure on the terminal building.
And asked whether passengers had seen the end of marquees, Mr Nelson said: "We can't guarantee that right now".
Some escalators and toilets, were not up to scratch he added.
Heathrow chief executive Tony Douglas said that his airport had already recruited 500 security staff,
1965: BAA set up to run Heathrow, Gatwick, Stansted and Prestwick airports
1971: Bought Edinburgh airport
1975: Bought Glasgow airport
1990: Bought Southampton
1992: Sold Prestwick
2000: Competition review approves continued ownership of three London airports
2006: A group headed by Ferrovial buys BAA for £10bn
He acknowledged other problems at the airport, including keeping it clean, which he said posed "challenges".
Mr Douglas added: " There is no question that customer service at Heathrow has been unacceptable and at times it continues to be unacceptable."
The new Heathrow Terminal Five is due to open in a year's time.
BAA, which served nearly 150 million passengers in 2006, was last year taken over by a group headed by Spanish airport operator Ferrovial.
Among its plans are the building of a second runway at Stansted - projected to cost about £2.7bn - which would more than triple the number of passengers to 75 million by 2030.
It is currently facing two probes by the Competition Commission - including one over how much it can charge airlines to use Heathrow and Gatwick airports.