Stephen Nelson joined BAA from Sainsbury's

He will be replaced by Colin Matthews, who led the restructuring of water company Severn Trent, from 1 April.

Mr Nelson joined BAA in 2005 from Sainsbury's, where he was marketing director, and has been BAA's chief executive since 2006.

He said that BAA had faced "considerable challenges" during his time at the company.

"I am immensely proud both of the way the company responded to those challenges, and refocused its efforts to put the passenger first," Mr Nelson said.

I am determined to continue to raise standards across all our airports Colin Matthews, new BAA chief executive

He presided over the introduction in August 2006 of stricter hand baggage restrictions, which led to long delays at airports.

Last week, the Association of European Airlines said passengers using airlines at Heathrow suffered the worst flight delays among all leading European airports.

'Challenging' job

"I am determined to continue to raise standards across all our airports," new chief executive Colin Matthews said.

"No-one underestimates the size of that challenge, or the difficulties we face on a daily basis in delivering it," he said.

He will join at a time when BAA is under scrutiny from competition authorities and pressure from environmental campaigners.

The Competition Commission is investigating the operator, whose airports handle 60% of the UK's air travellers. There has been speculation the company may be split up.

BAA's UK AIRPORTS Heathrow Gatwick Stansted Glasgow Edinburgh Aberdeen Southampton

This week, environmentalists have carried out protests at Heathrow and the House of Commons against the proposed third runway at the UK's busiest airport.

"There is no doubt there is pressure on the airports as never before from increasing passenger numbers on the one hand and from environmentalists on the other," Mott McDonald's aviation consultant Laurie Price said.

"The new chief executive will have to walk a tightrope while recognising the interests of government, competition and his shareholders," he said.

BAA operates seven UK airports, including Glasgow and Southampton. Latest figures show its airports handled 10.9 million passengers in December 2007.