Grant was allegedly drunk when he was seen making out with an unidentified woman for about 20 minutes, while a male friend caressed her thigh at the bar of a Japanese restaurant, the Mirror reported Friday.
"It was disgusting. Hugh and the girl were completely going for it. It was brazen. But he didn't seem to care," witness Hannah Crow told the newspaper. "Weirdly, the other guy tried to appear as if he wasn't doing anything. I've never seen anything like it. It wasn't normal."
When the Mirror went to Grant's London home to get a comment from him, he allegedly yelled "F-off" through an intercom.
Grant, Elizabeth Hurley's former long-time boyfriend, made headlines in 1995 after he was arrested for lewd conduct in a public place with a prostitute.
The actor has appeared in the films "Four Weddings and a Funeral," "Sense and Sensibility," "Notting Hill," "Mickey Blue Eyes," "About A Boy," "Love Actually," "American Dreamz" and the two "Bridget Jones" films.