The 34-year-old TV star was spotted holding hands and talking with the rugby star at Mahiki nightclub in London after posing for a photo shoot together on Tuesday (04.12.12).
In the club, Kate - who has apparently "fancied" Gavin, 30, for a long time - made no secret of the fact she was impressed with his muscles and gave his bulky frame a good squeeze.
A source told the Daily Mirror newspaper: "Gavin is Kate`s type. She has fancied him for years.
"They got on well at Mahiki. She squeezed his arms and started `phwoaring`. They spent most of the night in the club`s private room."
The photographer from the shoot revealed there was definite chemistry between the pair while they were working together, posting online: "Just finished the Jordan/GavinHenson job. That was insane. Fair to say - he pulled!"
After flirting in Mahiki, Gavin asked Katie to join him for dinner and they headed to Balans restaurant where they drank cocktails and ate Thai chicken curry.
The source added: "Gavin suggested dinner so Kate took him to her favourite restaurant where they drank porn star martinis and flirted. They were snogging within minutes. They swapped numbers and plan a more discreet date next week."
Katie - who has two children, Junior, seven, and five-year-old Princess Tiaamii, with ex-husband Peter Andre, and 10-year-old son Harvey, with ex-boyfriend Dwight Yorke - recently split from her fiance, Argentinean model Leandro Penna.
Gavin was previously engaged to singing sensation Charlotte Church, 26, with whom he has two children, five-year-old Ruby and Dexter, three.