The see-through dress which sparked Prince William's interest in Kate Middleton sold tonight for £78,000.

The knitted gown, worn by Miss Middleton at a University of St Andrews fashion show attended by William in 2002, was auctioned in a packed central London sales room.

Auctioneer Kerry Taylor had estimated that the garment, which leaves little to the imagination, would sell for £8,000 to £10,000.

The cost of the dress, excluding the buyer's premium, was £65,000.

A man at the back of the sales room, who would not give his name, bought it on behalf of an individual he would only name as "Nick from Jersey".

The mystery bidder, who wore a quilted jacket and glasses and looked to in his mid-30s, was besieged by the press at the end of the sale but would not give his name.

But in response to the many questions about the buyer, he said: "He thinks it's an iconic piece and is very happy with the purchase."

Ms Taylor had started the sale at £20,000 and, for a few minutes, took ever-increasing bids made by phone via staff who sat along one side of the sales room.

But when the price reached around £50,000, the battle for the dress turned into a two-way tussle between the man at the back of the room and some bids pre-registered with the auctioneer.

When the figure hit £65,000, Ms Taylor waited a few moments before ending the auction to applause from the many buyers in the room.