A Union Flag, an EU Flag and a 'One Way' street sign are seen in London on December 8, 2017 | Leal Olivas/AFP via Getty Images EU demands delay to end of free movement post Brexit The proposed guidelines reopen a key provision on citizens’ rights agreed by the two sides in December.

EU diplomats are demanding further concessions from London, including delaying Britain’s right to bring in strict new immigration controls immediately after Brexit day, in exchange for a transition period that would save the U.K. from a Brexit cliff edge.

The demands are reflected in new draft negotiating directives aimed at setting the parameters for a transition period after the U.K.'s official exit date in March 2019.

In the draft, obtained by POLITICO, EU diplomats have proposed extending the deadline by which EU citizens living in Britain can claim a special residency status to the EU's preferred end for the transition of December 31, 2020 — 21 months after the U.K.'s official withdrawal date.

By effectively delaying an end to freedom of movement between the EU27 and the U.K., the proposals would block the U.K.'s ability to introduce new immigration controls on EU migrants until that date.

The tougher stance signaled in the draft risks making it harder for Prime Minister Theresa May to sell a deal at home, where she is still hostage to a faction of Brexiteer Conservative MPs and to the Northern Irish Democratic Unionist Party, which props up her government and also takes a tougher line on Brexit.

A U.K. government official close to the negotiation declined to comment. The European Commission and Council did not respond to a request for comment.

A senior Brexit-supporting Conservative MP, speaking on condition of anonymity, warned that the EU’s new demand “might very well be a deal breaker.” Immigration was a key part of the offer to voters from the Leave campaign during the EU referendum.

“I would very much hope that this is not the final position, since it makes a ‘no deal’ outcome all the likelier,” the MP said. “Also the hardening of their position on trade deals isn’t helpful. If we leave without an agreement, it’ll cause them problems with third countries.”

The broader window for citizens and family members to claim the special protections (called "settled status") is just one of several tougher conditions for a transition deal that were included in the new draft of the negotiating directives. But the change of date would cut both ways — U.K. citizens living in the EU would also have their rights extended.

Such directives are subject to a near-constant process of revision up until they are approved by ministers or directly by the European Council, and they could well change again before a key meeting of the EU's General Affairs Council on January 29, at which they are expected to receive final sign off.

The directives tighten language making clear that during the transition, the U.K. will still be bound by the EU's international agreements, and emphasizing that "the United Kingdom may not become bound by international agreements entered into in its own capacity in the fields of competence of [European] Union law, unless authorized to do so by the [European] Union."

The EU27’s demand to revisit terms of the Phase 1 divorce agreement potentially opens up Brussels to charges of negotiating in bad faith.

Brussels is in an extremely strong bargaining position when it comes to the transition arrangements given the potential damage to British businesses and the overall U.K. economy of a cliff-edge scenario — and the pressure the U.K. government is coming under from businesses to secure a quick deal. But the EU27's demand to revisit terms of the Phase 1 divorce agreement potentially opens up Brussels to charges of negotiating in bad faith.

The initial terms of the divorce accord were clinched just over a month ago, and involved a flurry of 11th-hour negotiations with May's direct involvement. That Phase 1 agreement included terms that many supporters of Brexit regarded as steep and undesirable concessions, particularly on the financial settlement by which the U.K. will continue contributing to the EU budget as if it were a member.