BAA owns Scotland's three largest airports, in Edinburgh, Glasgow and Aberdeen, as well as Heathrow, Stansted and Gatwick in London.

Today's announcement follows a report from the Competition Commission last month which identified "significant competition problems" because of BAA's dominant position and proposed the company cease running two of its three London airports, as well as either Edinburgh or Glasgow. The CC found that BAA's airports account for 88 per cent of passengers in Scotland.

Colin Matthews, BAA's chief executive, said: "When the Competition Commission published its provisional findings, we said that we would be realistic in our response, though we disagree with the Commission's report and the analysis on which it is founded.

"We will continue to present our case, in respect of the south-east airports and those in Scotland.

"Our response to the report, and our announcement concerning Gatwick, is intended to focus our efforts accordingly."

If the proposals are rubber-stamped in the final report at the end of the year, BAA will have to look at disposing of one its Scottish airports.

BAA Scotland's Gordon Dewar, who is due to become Edinburgh Airport's MD this month, argued that Edinburgh and Glasgow airports serve separate markets.

BAA said it was beginning the sale process at Gatwick "immediately".

The move has come under fire from the Unite trade union, which represents airport workers.

Steve Turner, Unite national officer, said: "Gatwick is a core component of the national infrastructure and an essential part of the UK's aviation sector yet it is to be flogged off with little care for the wider social impact.

"This is devastating news to the many hundreds of loyal and dedicated staff at Gatwick."

Analysts say the sale of Gatwick could fetch between £2 billion and £3 billion. Virgin Atlantic said it would be happy to join a bidding consortium.