A letter informing relatives of a Hove airman who was killed in the Dambusters' raid was withdrawn from sale after it was found to be fake.

The typed six-paragraph letter about Flying Officer William Tytherleigh, 21, of 4 Portslade Villas, Hove, was dated May 20, 1943.

It was signed by Wing Commander Guy Gibson who led 617 Squadron which targeted the Mhne and Eder dams in Germany with bouncing bombs.

Gibson, who won the Victoria Cross for leading the raids, was only 26 when he was killed in the Netherlands a year later, giving the letter particular value and it was expected to raise at least £6,000.

The letter stated: "It is with deep regret that I write to confirm my telegram advising you that your son is missing as a result of operations on the night of May 16/17, 1943.

"Your son was front gunner of an aircraft detailed to carry out an attack against the Eder Dam. Contact with this aircraft was lost after it took off, and nothing further was heard from it.

"It is possible that the crew were able to abandon the aircraft and land safely in enemy territory.

"The captain of your son's aircraft, Squadron Leader Maudesley, was an experienced and able pilot, and would, I am sure, do everything possible to ensure the safety of his crew."

Tytherleigh's Lancaster bomber, call sign 'AJ-Z for Zebra', was damaged after getting too close to the explosions on the ground on its third run over the Eder Dam. The crew died after the plane was shot down on its way home.

He was awarded a post-humous Distinguished Flying Cross and is buried in Germany.

Richard Westwood-Brookes, the documents specialist at Dominic Winter Book Auctions in Swindon, received the letter from a bona fide collector of military and aviation items who was selling the letter to raise money for a critical heart operation.

Mr Westwood-Brookes said: "When this letter arrived we had no reason to doubt its authenticity. It looked just right.

"We got quite excited about it. There are not many letters from such a glamorous person in the Second World War."

The firm decided to publicise such a rare letter in The Daily Telegraph and they received telephone bids of up to £6,000 in advance of the auction due to be held on June 14.

One hour after the Telegraph came out, they got a call from the sister of the Tytherleigh, Edith Widdowson, 77, who now lives in Halifax.

She said the address on the letter could not possibly be right, because they were not living there at the time.

Mr Westwood-Brookes got in touch with the archivist at Brighton who looked up the electoral register for 1937.

The family did not live at Portslade Villas; in fact the address does not exist at all. They lived at 24 Hova Villas, Hove.

When it emerged Gibson had spelled the name of the Squadron Leader Maudsley wrong - who was his best friend - the expert decided to do more research on the letter and concluded it had to be a forgery.

Next week they will pass the letter and related details on to the Organised Crime Squad of New Scotland Yard for further investigation.

He said: "We are not in the realm of somebody doing a prank. We are not in the realm of somebody believing it was genuine. They had got a typewriter and paper and ink from the period and tried to get us to believe it.

"The vendor and the sister of the dead airman were very upset. We decided to take a stand on this. It is something which must be stamped out."