It had been reported that Cat - stunning in a simple, short red dress – was back on the market after Jack had broken up with her to concentrate on his film career.
The actor and grandson of legendary film director John Houston is due to appear in the new Twilight movie, Eclipse.
Jack, 27, and the Birmingham-born TV presenter were just two of the stylish celebs turning out for the London event.
Eva Herzigova, Donna Air, Jasmine Guinness and Jade Parfitt all went for glam festival wear of skinny jeans, but dressed up with statement clutches and high heels for the ‘Mini festival’ organised by Mini to launch its new Countryman car.
The event was held at a city farm in London’s Docklands set against the high-rise backdrop of Canary Wharf, complete with sheep adorned with graffiti signs.
Timbaland – best known for his work with Missy Elliott, Justin Timberlake and, currently, Katy Perry – debuted his latest collaboration, with Grammy award winning American country singer Michelle Branch, after bringing his daughter Rain on stage to greet the crowd.
The rap star said that he'd always wanted to do country. "I think country is great," he revealed. "It's more about the tunes than the beat and the song writing stays with you more.
"Every five years I try to come up with a new style and I actually think I have it right now."
Ronnie and Jo Wood's son Tyrone and designer Henry Holland also attended the party