BRUSSELS (AFP) - Theresa May confirmed on Friday (Dec 14) she had a "robust discussion" with European Commission President Jean-Claude Juncker, after footage emerged of the pair having a heated Brexit row at an EU summit.

As the leaders gathered in their conference room, the British prime minister was filmed by the EU's in-house TV crew confronting Juncker after he called the UK's position on Brexit "nebulous".

Instead of the anodyne pleasantries the leaders normally exchange in front of the cameras, a visibly angry May confronted Juncker to demand he explain his comments.

"What did you call me? You called me nebulous. Yes you did," May said according to lip-readers hired by Britain's Channel 5 News.

As Juncker puts his hand on May's arm to placate her, Dutch Prime Minister Mark Rutte is seen striding across the room to restore the peace.

British media swiftly characterised the incident as a "handbagging", recalling former prime minister Margaret Thatcher's strongarm tactics to win an EU budget rebate more than 30 years ago.

At a midnight news conference on Thursday after EU leaders rebuffed May's plea for help to sell her Brexit plan to sceptical lawmakers at home, Juncker demanded more clarity from London, saying in French "we are in a debate that is sometimes nebulous and imprecise".

May insisted there were no hard feelings after the exchange, which sent pulses racing at what was already a tense summit.

"I had a robust discussion with Jean-Claude Juncker. I think that's the sort of discussion you are able to have when you've developed a working relationship and you work well together," May said.

"What came out of that was his clarity that... when he used that particular phrase he'd been talking about a general level of debate."

Juncker later reiterated that he had not been referring to May personally and said he had not realised the word "nebulous" even existed in English.

"I did not refer to her but to the overall state of the debate in Britain," he told reporters, saying that watching the British parliament debate Brexit had left him unclear about where things were heading.

"I was not addressing her, and in the course of the morning after having checked what I said yesterday night she was kissing me," added Juncker, who is known for his affectionate and tactile approach to European leaders.