LONDON — Guy Verhofstadt was supposed to be the bad cop. No longer.

Behind the scenes in Westminster, the European Parliament’s Brexit coordinator is now seen as something of an ally on the future relationship between Britain and Brussels.

Of two approaches set out in Brussels this week, first by the Parliament in a draft resolution and then on Wednesday by European Council President Donald Tusk in draft negotiating guidelines, it is Verhofstadt’s that grabbed London’s interest.

Although the Parliament’s document contained a barrage of proposals and stipulations that run counter to the U.K.'s view of the future relationship, its framework was much closer to Theresa May’s vision set out in her Mansion House address last week — in particular, the idea of packaging up the future relationship as an “association agreement,” which is seen as allowing for a closer, more flexible and dynamic relationship after Brexit than the Council’s opening offer.

Tusk’s far more minimalist proposal, effectively rejecting most of the U.K. government’s plans, was seen by London as “something we can work with” but also unnecessarily restrictive and uncompromising. Its language ruling out British involvement in EU agencies was particularly irksome to London, one senior official said.

The transformation of Verhofstadt from hard-liner into potential U.K. ally would represent a remarkable turnabout, and the difference between his and Tusk's approach may hint at inter-institutional rivalries in Brussels that the U.K. can exploit.

At 13 pages, the Parliament’s draft resolution is more than twice the size of Tusk’s draft guidelines, and more detailed. And it also contains language that at times seems far more conciliatory than the Council’s draft guidelines, for example, by stating the need for close cooperation in areas like public health and medicines, and opening the door to continued U.K. cooperation with certain EU institutions, like the European Medicines Agency, through bilateral arrangements.

"As a third country the U.K. cannot participate in or have access to EU agencies,” the Parliament wrote, adding: “However … this does not exclude cooperation in specific cases.”

A spokesman for Verhofstadt said there was no difference in approach with the Council. "It's not a matter of good cop/bad cop,” the spokesman, Bram Delen, said. “The European Parliament wanted to find a way forward between the red lines of the U.K. government on the one hand and on the other hand the principles of our Union as repeated by the Council and with which we fully agree.”

Delen said the Parliament’s proposal was rooted in provisions of the EU treaties, specifically articles calling for “a special relationship with neighboring countries” and authorizing association agreements “involving reciprocal rights and obligations.”

“We looked at what the treaty prescribes, specifically Articles 8 and 217,” Delen said. “This enabled us to outline a more detailed proposal: an association agreement with four pillars and including mutual rights and obligations.”

The framework of an association agreement with the European Union after Brexit is now being seriously considered in Whitehall. It is facing the challenge of how to bind Brussels as much as possible into following through with commitments made during the Brexit talks, when negotiations on a free-trade deal cannot even be started formally until after the U.K.’s withdrawal.

"There are a variety of legal instruments which can deliver the ambitious partnership we are seeking. An association agreement is one which has been used by the EU previously and provides a clear framework that can encompass a wide-ranging relationship," said a senior U.K. government official.

The EU typically signs such association agreements with prospective member countries and other partners, and London believes that using the model could give a formal structure to the “political declaration” that negotiators on both sides have said will lay out the consensus view on the future relationship and be published alongside the formal withdrawal treaty.

Article 50, which sets forth a bare-bones procedure for a country to leave the bloc, calls only for the withdrawal agreement to take account of the framework of the future relationship expected with the departing country. But it does not offer any specific instructions on how to do that.

With such legal ambiguity, it is unclear whether the EU would go along with drafting an association agreement, or even allow that such an agreement could be signed with the U.K. while it is still a member of the bloc.

Asked about the possibility on Wednesday after Tusk put forward the new draft guidelines, a senior EU official said: “As for association agreement, that's about the legal form of what we adopt in the end. I think it's much too early to address that.”

The EU27 have ample motivation to keep the discussion of the future relationship as general as possible. Firmly ruling out some of the U.K.’s top demands, such as an agreement on access to the EU market for Britain’s financial services industry, might hurt the chances of concluding the withdrawal treaty.

Verhofstadt, by drafting the detailed Parliament resolution on the future relationship, may have inadvertently given the U.K. a cudgel to use against the Council and the EU negotiators in the European Commission, who might be hard-pressed to argue against formalizing whatever is agreed in the talks — especially if it is done in a format endorsed by the European Parliament.