British Prime Minister Theresa May has not moved "an inch" on her Brexit "red lines," Labour's top legal policy chief Shami Chakrabarti said on Sunday, suggesting there was little hope of a quick breakthrough before an EU summit.

"So far, our impression is that Mrs. May hasn't moved an inch on her red lines ... In substance, as yet, there's been not a jot of movement from the government," Chakrabarti told Sky News.

"It seems to me that this has been left so late in the day. ... It's hard to imagine that we are going to make real progress now without either a general election or a second referendum on any deal she can get over the line in parliament."