Although there have been a number of attacks by "Rolex robbers" in London over the past three years, police say there was no reason to link this attack to others. Previous victims include the Formula One chief Bernie Ecclestone and the actress Britt Ekland.
The latest victim, Ivor Jacobs, 38, from Ockbrook, in Derbyshire, was sitting with his daughters, Danielle, 12, and Roxy, eight, in a Range Rover in St Martin's Lane. The television presenter Anthea Turner was in the front passenger seat and her boyfriend, Grant Bovey, was driving.
The suspect opened the kerbside rear door and clambered over the children before trying to snatch the Rolex, thought to be worth pounds 25,000, from Mr Jacobs's wrist.
A police spokeswoman said: "A struggle ensued. However, the suspect managed to release the clasp of the watch." One of the children was slightly burned by the attacker's cigarette. Officers think the man might have waited in the foyer of the Cambridge Theatre, where the party had watched the musical Grease, and followed them to a Planet Hollywood restaurant.
The suspect was described as black, aged about 25, six foot tall and thin.
He wore a navy blue jacket, a dark blue jumper and dark blue jeans. He was seen running away towards the Seven Dials area of nearby Covent Garden.