Singapore Airlines is in talks to sell its 49 percent stake in British carrier Virgin Atlantic, with sources saying Delta Air Lines, with sources saying is among the suitors keen to access Virgin’s lucrative slots at London’s Heathrow airport.

Richard Branson’s Virgin Group wants to keep its 51 percent stake in Virgin Atlantic and work with Delta if the U.S. carrier pulls off a deal, a source familiar with Branson’s thinking added.

Singapore Airlines said in a brief statement it was in talks with interested parties but did not name them. It also cautioned the discussions might not result in a deal.

Airlines like Delta have long hoped to break into London’s capacity-constrained Heathrow airport, a lucrative hub for corporate passengers where landing slots are generally hard to acquire. Virgin Atlantic is the second-largest carrier at Heathrow after IAG’s British Airways.

Delta has been considering ways to partner with Air France-KLM, which could also take a stake in Virgin Atlantic, one person familiar with the matter said.

The European Union requires that EU carriers be under European control, meaning Delta would need an EU airline as a partner if it wanted majority control of Virgin Atlantic.

If Air France-KLM were to buy a small percentage of Branson’s stake, then Virgin Atlantic could continue to be European controlled. However, the source close to Branson signalled the British entrepreneur was not looking to sell.

“As far as he (Branson) is concerned, it is just Singapore Airlines’ 49 percent stake that is up for sale - he is keen to maintain control of Virgin Atlantic and form a stronger airline,” the source said, adding Branson supported a deal with Delta because it would make Virgin Atlantic stronger on routes between Britain and the United States.

Delta, the second-largest U.S. airline by revenue after United Continental, has been looking to acquire a stake in Virgin Atlantic for more than two years but previous talks broke down over price and other issues, and there is no guarantee that its recent discussions would result in a pact, two people familiar with the matter said.

“London obviously is the premier market and Heathrow is by and large the market leader. It’s the lynchpin transatlantic market in terms of size and revenue, particularly premium traffic revenue,” said George Hamlin, an aviation consultant in Fairfax, Virginia.

A deal with Delta would also give Virgin Atlantic access to hundreds of markets on a one-stop connecting basis in the United States, he added.

Delta and Air France-KLM declined to comment.

“We are always talking to many airlines on a number of different matters but we never comment on the details of these discussions,” a Virgin Atlantic spokeswoman said.

If Delta succeeds with its bid, Virgin Atlantic, which is not a member of a global airline alliance, would almost certainly join Delta and Air France’s SkyTeam, the source close to Branson said. SkyTeam trails its oneworld and Star Alliance counterparts in slot access at Heathrow.

“Delta now finds itself going up against the combination of American Airlines and British Airways,” said Hamlin, referring to the two anchor members of the oneworld global alliance.

“British Airways brings along a feed from other destinations - both Europe and intercontinental - at Heathrow. Delta is basically a dead-end at this point.”

Virgin Sale Option

Singapore Airlines (SIA) bought 49 percent of Virgin Atlantic for 600 million pounds ($962 million) in 1999, but has been open to selling its stake since at least mid-2011 when a price of $500-$600 million was mooted in markets, a banking source familiar with the talks said at the time.

At the same time, SIA has been refocusing on its key markets where it is under pressure from low-cost airlines, launching its own budget carrier, Scoot, and bolstering its Asian regional carrier, SilkAir.

Virgin Atlantic, like other European carriers, has been battered by rising fuel prices and the euro zone crisis, and posted a loss of around 80 milli