European Commission chief Jean-Claude Juncker said it would take 'miracles' for Brexit divorce talks to make enough progress by the end of October to move on to trade negotiations.

"By the end of October, we will not have sufficient progress," Juncker said as he arrived for an EU summit in Tallinn. "I'm saying there will be no sufficient progress from now until October unless miracles happen."

EU leaders are set to decide at a summit on October 19-20 whether there has been "sufficient progress" on the divorce to start discussing the future relationship, including a trade deal, as Britain has demanded.

But British Prime Minister Theresa May insisted there had been "very good progress" on the rights of EU expatriates, following a major Brexit speech she gave in Florence, Italy, last week.

"In my Florence speech, I set out very clearly how we could ensure that the rights of those EU citizens were guaranteed in the UK," May told reporters. "That has been part of the negotiations that we've had, very good progress has been made, that was made clear by the statements made by David Davis and Michel Barnier on Thursday," she added.