MPs are concerned that Theresa May will present a vague, wishy-washy Brexit deal to Parliament in order to deter potential opponents from voting it down.

However, Michel Barnier has reassured British MPs that the EU side wants any detail to be "detailed" before it is signed off, BI can exclusively reveal.

The EU will not allow "some vague, apple-pie declaration," a well-placed source told Business Insider.

LONDON — European negotiators will insist that Britain must agree "detailed" terms on Britain's future relationship with the EU, in plans that would scupper any attempt by Theresa May to avoid parliamentary defeat by only offering MPs a vote on a vague "declaration of intent" deal.

The prime minister has insisted that MPs will be given a "meaningful vote" on whatever deal May secures from Brussels in October.

However, MPs have repeatedly expressed concern that the prime minister will instead seek to present MPs with a vague so-called "heads of agreement" deal, which would only offer a vote on a non-legally binding "statement of intent" ahead of more detailed agreement with the EU after MPs have voted.

EU sources have told BI that the EU's chief negotiator Michel Barnier is set to oppose any attempt to put such a limited deal before MPs.

One source close to EU chief negotiator Michel Barnier told Business Insider that he will insist that there must be "clarity" on any deal presented to parliament.

"The goal of the Chief Negotiator Michel Barnier is to have a declaration in October that creates clarity on the future relationship," the source told BI.

Business Insider understands that senior EU figures are concerned that a "heads of agreement" deal would allow Britain to renege on commitments made during the negotiation.

"The member states don't want a situation where we get something very vague signed off by the UK Parliament in October and EU Parliament in February, and then the British government tries to use the transition period to unpick what was agreed. It would be a constitutional crisis," one British MP who has met with Barnier in recently told BI.

The UK parliament's Brexit select committee met with negotiator Barnier and the European Parliament's chief Brexit co-ordinator Guy Verhostadt this week and was told the EU would insist on explicit "detail" on Britain's future relationship before any deal is signed off.

"They [Barnier and Verhofstadt] both said they recognised the need for detail," one MP on the committee told BI, adding that Barnier had made it clear that the final deal would not amount to "some vague, apple-pie declaration."

The source added: "That's exactly what the heads of state and government of the EU27 want as well. They want detail. They don't want any surprises."

The intervention comes amid concern among Remain-backing MPs that they will not be given a "meaningful" vote in October.

Conservative MP Anna Soubry quizzed the prime minister in December on whether she planned to only present a "heads of agreement" deal to parliament, but did not receive a clear answer to the question.

Former Deputy Prime Minister, Nick Clegg, also raised this concern in an interview with Business Insider in January.

"If MPs swallow their misgivings and simply sign along the dotted line, even though the government clearly has no intention of providing MPs with much meaningful detail for what the future holds, then at that point the Brexit juggernaut will proceed without any further meaningful restraint or scrutiny," Clegg said.

"Managed divergence"

Prime Minister May has been clear that Brexit will mean Britain will leaving the single market, customs union and jurisdiction of the European Court of Justice.

However, big questions remain on how it plans to maintain tariff-free trade with the EU outside the single market, as well as avoid a hard border between Ireland and Northern Ireland outside the customs union.

On Thursday night, Cabinet members reportedly reached an agreement that Britain should aim for "ambitious managed divergence,"but this phrase fell short of answering the aforementioned questions and more.

Donald Tusk, EU Council President, rejected the phrase on Friday night. He said: "I’m afraid that the UK position today is based on pure illusion. It looks like the cake philosophy is still alive."

A senior EU source described the plan to BI as "ambitious" and a "sticking plaster for the Tory party."

Pro-EU campaigners said the prime minister must not attempt to offer MPs a "cake and eat it" deal.

Eloise Todd, CEO of anti-Brexit group Best For Britain, said: "Theresa May will have to be clear about where the Brexit deal will end up in order for the vote to be meaningful.

"A cake and eat it Brexit will not be possible. Clear decisions will have to be made on the Irish border in the coming weeks, let alone by the Autumn. If the destination is bad, or unclear, or both, even more reason for Brexit to be put to the people of the country."