The unlikely pair, who attended the Prince's Trust Future Investment gala dinner at London's Camden Roundhouse earlier in the evening, headed to the Dorchester Hotel together before being taken to Knightsbridge.

Naomi and Lewis quickly stocked up on cigarettes and were last seen being driven to Kensington.

One source said: "They were quite touchy feely with each other before they realized they were being watched, but as soon as they saw the photographers they hid their faces and tried to get as far away from each other as possible."

"It was like they had something to hide."

Naomi's spokeswoman insists the supermodel isn't dating Lewis, saying: "They are just friends."

"Naomi did a photoshoot in the afternoon with him, and they decided to go to the event together in the evening along with Lewis' dad."

The couple sparked romance rumors earlier this year when Naomi "flirted outrageously" with Lewis at the GQ Man of the Year awards.

Naomi fueled speculation after she flew out to Brazil last month to see Lewis finish second in the Formula One Championship.

Lewis was rumored to be romancing the Pussycat Dolls singer Nicole Scherzinger earlier this year, while Naomi has had high-profile relationships with P. Diddy and Flavio Briatore.