Ferrovial, the owner of British airports operator BAA, has whittled down the shortlist of bidders for its Edinburgh airport to four and will accept final offers in early April, according to sources with knowledge of events.

Global Infrastructure Partners (GIP), JP Morgan Asset Management and consortiums led by Carlyle Group and 3i have made it to the second round after a longer list was cut down in recent days, said one source close to the sale.

They will be taken onto due diligence next and final offers are due in by early April.

BAA put the airport up for sale last year, bowing to an order by Britain's Competition Commission to sell either Edinburgh or Glasgow airports as well as London's Stansted and Gatwick airports to increase competition.

Analysts expect Edinburgh airport, which handled 9.4 million passengers last year -- up 9 percent on 2010 -- to fetch between 500 million pounds and 700 million pounds.

Edinburgh airport had earnings before interest, taxes, depreciation, and amortisation (EBITDA) of about 50 million pounds in 2011 and airport assets generally get sold for up nine or 10 times EDIBTA, another source close to the process said.

BAA sold London's Gatwick, the country's second largest airport, to GIP for 1.5 billion pounds in 2009 as part of the CC's original ruling.

BAA owns London's Heathrow, Europe's busiest airport, as well as Southampton and Stansted in England and Glasgow, Edinburgh and Aberdeen airports in Scotland.

BAA is owned by a consortium of institutional investors led by 49.9 percent shareholder Ferrovial, the Spanish transportation infrastructure group.

The airport operator announces full-year results on Wednesday.

(Editing by Greg Mahlich)