Former Tory premier Sir Edward Heath was in a London hospital last night after falling ill during a visit to Austria.

The ex-MP was flown by air ambulance from Salzburg yesterday after suffering a suspected pulmonary embolism - a blood clot on the lung.

A spokeswoman from the Tyrolean Air Ambulance, based in Innsbruck, confirmed that Sir Edward had been flown to London's RAF Northolt airbase after being picked up from Salzburg's main hospital. She said that he travelled with their medical team and his private secretary, but would not comment on his medical condition.

It was rumoured that Sir Edward, 87, was taken to the private King Edward VII hospital in central London.

A hospital spokeswoman said she could not comment on individual patients, but that they had been told to refer any calls regarding Sir Edward to his private secretary.

Although the seriousness of his condition is unknown, it is understood Sir Edward was well enough to give instructions to his staff.

Pulmonary embolism is a condition commonly associated with so-called "economy class syndrome" or deep vein thrombosis.

Rumours about the health of Sir Edward have been circulating in Westminster for several weeks.

He left the Commons at the 2001 election after serving as MP for Bexley and Old Sidcup for 51 years.

A non-smoker who rarely drank, he has remained in good health throughout his life.

The lasting legacy of Sir Edward's premiership from 1970-74 was to lead Britain into Europe.

In 1975, the year after being defeated by Labour, Sir Edward lost the party leadership to Margaret Thatcher in a ballot of Conservative MPs. He went to the backbenches, refusing to serve under her.

Sir Edward, who was knighted in 1992, never forgave Mrs Thatcher.