And fittingly, Cameron decided to wear a British design for the occasion – a cute sparkly minidress by Stella McCartney.
The outfit perfectly showed off her endless legs – made even longer with the addition of vertiginous black peep toe stilettos.
The blonde star – who like Tom, spent a good deal of time meeting some of the hundreds of fans who had turned up to Leicester Square – had earlier suffererd a mishap has the pair filmed a segment for motoring show Top Gear.
She was taking part in the 'Star in a reasonably-priced car' section – wherein celebrities have to complete a lap of a circuit in a regular car in the fastest time possible.
But the 37-year-old experienced a problem with the clutch in her red Kia, and the car came to a halt in the middle of the Surrey race track.
She was rescued by the BBC2 programme's mysterious Stig, whose job it is to train up the celebrity contestants.
Tom, meanwhile, completed his lap without incident, though it's not known if he beat the winning time, currently held by Harry Potter star Rupert Grint.
Famous faces turning out to see the action adventure included former X Factor contestant Stacey Solomon - who brought along her mum - and Boyzone singers Keith Duffy and Shane Lynch.