James Bond's geiger counter wristwatch from Thunderball has turned up at a car boot sale, following years of mystery about its whereabouts.

The prop – one of many gadgets used by 007 during his half-century on screen – was key to the plot of the film as it helped the agent locate stolen atomic weapons during underwater scenes in the 1965 film.

The Breitling watch was picked up for £25 but is now to be sold by Christie's in London with an estimated price of up to £60,000.

The Top Time model by the luxury Swiss watch firm was the first watch adapted by Q's team of boffins in the film series. One of the hands of the watch shows the strength of radioactivity.

The basic watch was originally made by Breitling in 1962, then adapted. It was the only one produced for the movie, and it is thought it had been passed on by someone who worked at Pinewood Studios.