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Sky News has the story:

Tornado jets have escorted a New York-bound Olympic Airways passenger jet into Stansted Airport after a bomb alert.

Sky's James Matthews said the pilot called through a 'mayday' because he believed there was a bomb on board.

"The plane was flying from Athens to New York when it was diverted to the Essex airport.

The passengers have been escorted from the plane.

It is not clear yet whether a device has been found.

A Stansted airport spokesman said the plane was diverted under "full emergency conditions".

An RAF rescue helicopter is in the vicinity, Matthews said.

"It does not get very much more serious than that," said Matthews.

"The pilot thought it was serious enough to call in an escort. This may be the first time this has happened in British airpspace. The alert is very much full scale.

"My understanding is that he would have said there was nothing less than there is a bomb on the plane."

Update: BBC is reporting that the incident is "over" but there are no details on that so far.

Update:

A spokesman for Stansted Airportsaid the plane landed under "full emergency conditions."

The BBC's Athens correspondent Richard Galpin told BBC News 24 the incident happened after an elderly man called a Greek newspaper anonymously and told them there was an bomb on board.

The paper called the police, who called the airline. No code word is believed to have been used.

The plane, which was carrying 290 passengers, landed safely.

The RAF is not releasing any more details of how many of its planes were involved for security reason.