There will be "complexities and difficulties" in the Brexit negotiations, British Prime Minister Theresa May has been told in talks with senior members of the European Parliament.
It comes as Downing Street rejected suggestions a final deal could take a decade.
The prime minister met the parliament's president and lead Brexit negotiator in Brussels as the European Union's focus turned to preparation for the process of the UK's separation from the bloc.
In a highly symbolic event later, May's counterparts from the 27 other EU nations will meet without her in order to agree how to manage the Brexit talks.
But a turf war between the leaders, the European Commission's officials and the European Parliament threatened to derail the entire process.
Meanwhile, Downing Street insisted the Brexit process could be completed within two years after the UK's ambassador to the EU privately warned it could take a decade to finalise and even then may fail to be ratified by member states.
Number 10 said Sir Ivan Rogers, who spoke to May earlier, was passing on the views of other EU nations.
"Ivan is there to report the views of others, he is doing the job of an ambassador," a source said.
"He was representing what others are saying to him."
Downing Street indicated the government believes it will be possible to complete both the "divorce deal" and a new trade agreement within the two-year timeframe set out under Article 50 of the EU treaties.
"We have been clear it's a two-year process and we are not looking to extend it," the source said.
Footage from the start of the Brussels meeting showed May standing alone, and she will be outside the room as the other 27 leaders discuss their approach to Brexit over a dinner which has been delayed by overrunning talks.
May insisted it was right for the leaders of the other EU countries to meet in Brussels without the UK to thrash out their plans for handling the Brexit talks.
The "informal" discussion, which will take place after the prime minister has left the summit, is expected to see the European Commission's Michel Barnier given the main role in the negotiations.
