Proposals, due for publication on Tuesday, will be as vague as possible in order to force UK to explain what it wants

The EU will keep its draft guidelines for a post-Brexit trade deal as short and general as possible, the Guardian understands, in order to force Theresa May to explain what the UK wants and leaving the door open for a British shift on the customs union and single market.

The publication of the EU’s draft guidelines on Tuesday will be a stark moment for the prime minister, as it is made clear that a whole range of proposals made by May in her Mansion House speech on Friday are to be rejected.

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The document will, however, fall short of providing any kind of detailed plan, due in part to a lack of substantive discussion among the member states on the issue, but also reflecting a hope that the UK’s position would develop in time, senior EU sources said.

An EU diplomat involved in drafting the position of the 27 member states said: “They will say explicitly or implicitly that the guidelines have to be short and general. If the UK position develops then we will be able to develop our response.”

The Labour party’s shift in support of a customs union post-Brexit last Monday was warmly received in Brussels and there is an awareness of the precarious position May finds herself in parliament.

Labour believes there may be enough support to win a cross-party amendment to the taxation (cross-border trade) bill and the trade bill which would commit the UK to seeking a deal “which enables the UK to participate after exit day in a customs union with the EU”.

May’s speech on Friday fell flat in Brussels, where it was felt the prime minister was still seeking the benefits of the single market without accepting the obligations to accept the primacy of EU law, jurisdiction of the European court of justice and the free movement of goods, capital, services and labour. She also failed to offer any new thinking on how to avoid a hard border on the island of Ireland.

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“It is good to hear that the UK wants to stay in regulatory alignment but that doesn’t really solve any problems,” said one diplomat involved in drafting the EU’s position. “It doesn’t take us over the line. We are ships passing each other in the night. We are not connecting.”

Aleš Chmelař, the Czech Republic’s state secretary for European affairs, said: “We all want a good deal but it really does depend on the UK’s red lines.”

An hour-and-a-half “wrap-up” meeting of EU diplomats for the EU27 – who have been discussing the bare bricks of a future deal since December – concluded shortly before May’s speech started on Friday. However, sources said it was unthinkable that the basic thrust of the EU’s position would be altered by the prime minister’s words.

It will be made clear that the call for a mutual recognition of regulatory frameworks and Swiss-style membership of EU agencies, including the European aviation safety agency, will not be possible with the UK outside the single market.

In the field of financial services, which is key to the British economy, the UK’s demand for a “collaborative, objective framework that is reciprocal, mutually agreed, and permanent” to give certainty over the future for service providers in the City will go wanting.

The EU is expected to link access to UK waters for its fishing fleet to British seafood exporters having tariff-free access to the European market.

On a trip to see Danish fisherman in Jutland on Saturday, Michel Barnier warned that the British fishing industry could lose access to the European market if EU fishermen lost access to UK fishing waters. The two things “are clearly linked,” the EU’s chief negotiator said. “Our access to British waters and the British access to our market.”