Britain must give Brussels a clear Brexit blueprint to allow negotiations to move forward, according to the European Union’s chief Brexit negotiator.
All those involved "know where the EU stands" but "more clarity" is still needed from the UK, Michel Barnier said.
In a speech in Hannover in Germany, Mr Barnier said it was up to the UK government to come up with its vision for the future that either finalised or changed the UK's red lines.
"It is now up to the UK to come up with its vision for the future, which should confirm the UK's red lines or adapt them," he said.
"Once we have more clarity from the UK, we will prepare a political declaration on the framework for the future relationship to accompany the withdrawal agreement in the autumn."
It comes as UK Prime Minister Theresa May’s government suffered three more heavy defeats in the House of Lords over its flagship Brexit legislation.
In the main reverse, peers backed a cross-party move to retain key EU human rights provisions on exiting the union.
Earlier, Mrs May was forced to again insist the UK must leave the customs union after Brexit in order to strike trade deals around the world after a massive defeat on the issue in the Lords.
Both sides want plans for future relations to be set out by October along with a legally-binding treaty detailing the terms of the UK's withdrawal agreement.
Mr Barnier said the EU had made clear it wants a partnership that is as close as possible, but Britain's position on quitting the single market and customs union along with other policies meant it is "closing doors".
"The European Council has made clear that, if the UK's red lines were to evolve, the union would be prepared to reconsider its offer," he said.
"We are flexible, never dogmatic. We are open for business. But of course any change from the UK must respect our principles, the principles we have built with the UK over 45 years.
"In particular, the four freedoms of the single market go together. They are all indivisible.
"You cannot have free movement of services without free movement of goods, and so forth. And you cannot have free movement of goods without free movement of people."
Speaking on a local election campaign visit yesterday, Mrs May insisted that would not change course.
She said arrangements that are as "frictionless as possible" with the EU and the ability to strike trade deals around the world were both achievable under the proposals set out by her government.
Downing Street insisted the government's position had not changed since Mrs May delivered her Mansion House speech in March.
Those plans included two options, either a "customs partnership" effectively collecting duties for Brussels for goods arriving in the UK, but intended for EU markets or a "highly streamlined" arrangement making use of technology and regulatory co-operation.
But Mrs May is set to face calls from leading Brexiteers Boris Johnson, David Davis and Liam Fox to abandon her preferred form of customs deal, according to The Times newspaper.
A showdown is expected to come at a meeting of the cabinet Brexit committee scheduled for tomorrow when the trio will tell Mrs May that the "customs partnership" would be unworkable, the report said.
Mrs May will be given an indication of the scale of the opposition she faces from pro-EU Tories over her customs union plan in a Commons debate tomorrow.
Though the looming Commons vote on a pro-customs union motion would be a symbolic, non-binding one, it has the potential to deepen Tory wounds on Brexit.
Mrs May's spokesman played down its significance, saying the event was a "routine backbench business debate".
But binding Commons votes on a customs union during debates on the Taxation (Cross-border Trade) Bill and European Union (Withdrawal) Bill will prove harder for Downing Street to dismiss.