The submarine car used in the James Bond movie The Spy Who Loved Me fetched £550,000 at auction .
The Lotus Esprit, which was designed especially for an underwater sequence in the film, cost the equivalent of £300,000 to build.
The car, known on set as "Wet Nellie", sold for around £400,000 less than expected.
The distinctive-looking vehicle, which is said to be fully operational, was designed for the underwater scene in the 1977 film starring Roger Moore as 007.
It went under the hammer at RM Auctions in Battersea, south London where a female Bond fan was beaten in a bidding war by a telephone buyer.
The submarine car had been expected to fetch as much as £1 million having been called a "once in a lifetime" lot by the auction house.
Max Girardo, managing director of RM Auctions Europe, said: "We have a great track record in selling incredible and iconic movie cars, and this particular Lotus is certainly up there amongst the most famous cars of all time.
"Over the years, millions of movie-goers have stared in awe as the Lotus transformed itself into a submarine, and now, perhaps one of them will have an opportunity to own it. Her Majesty's Secret Service aside, it surely is the ultimate beach accessory."
Although six Espirit cars were used in The Spy Who Loved Me only one was turned into a fully operational submarine.