The Sherlock Holmes star was said to be "all over" former co-star Ruth Wilson when the couple were spotted kissing at London's Groucho club.
Law, 39, and Wilson, 30, co-starred at London's Donmar Warehouse last year in Anna Christie and it seems their friendship has blossomed into something more serious.
"They were quite enamoured with each other," says a source. "They were very tactile and seemed an item. They were kissing, and not worried about who saw them."
Jane Eyre star Wilson has said of Law: "He instantly disarms you because he's so generous and open."
Meanwhile, Law, who broke up with Miller, 30, a year ago, is looking for a new Manhattan pad.
"He wants to buy uptown as the penthouse he rents in the West Village is overlooked by New York University," says a friend. "Students were taking pictures of him sunbathing."
