MPs have delivered a highly critical verdict on British prime minister Theresa May’s controversial Brexit deal.

Elsewhere, Britain’s Brexit minister insisted a crucial vote on Mrs May’s Brexit deal would go ahead after a newspaper report on Sunday that she planned to delay it and make a last minute dash to Brussels to seek a better offer.

The Withdrawal Agreement and Political Declarations fail to offer enough clarity or certainty about the future, according to the Commons Committee on Exiting the European Union.

The cross-party report, released days before the Commons is due to vote on the deal on Tuesday, states: “After 20 months of negotiations, we only know the terms of the UK’s departure but not the nature of the future relationship with the EU.

“The Prime Minister’s deal fails to offer sufficient clarity or certainty about the future.”

The political declaration, which outlines aspirations for future relations between the UK and EU, is “neither detailed nor substantive”, meaning “significant uncertainty” remains about the terms of trade after a transition period, the study says.

“What is clear from the Political Declaration is that the extent of our access to EU markets will depend on the degree to which we adhere to its rules,” the report states.

The MPs said that government failure to set out objectives which are “realistic, workable, and have parliamentary support” mean that negotiations with the EU on the future relationship will be “further complicated, and could take significantly longer” than otherwise.

There are no “realistic, long-term proposals” on how to keep the Irish Border open while leaving the single market and customs union, according to the committee.

The backstop, which would keep the UK under EU customs rules to prevent a hard border in Ireland, would be implemented if London and Brussels do not agree a trade deal by the end of a transition period.

Activating the Irish Border backstop proposals would “result in immediate barriers to UK-EU trade in goods and services”, according to the study.

It states: “By July 2020 if the future relationship is not in place, or one/two years later if the transition/implementation period is extended, the UK could face the threat of significant economic disruption which would reduce its leverage in the negotiations.”

The committee also found that a Canada-style free trade deal with the EU would not be a viable option.

This is because such an agreement “would not ensure the type of friction-free trade with the EU that many UK companies with just-in-time supply chains need.”

Previously, committee member and prominent Brexiteer Jacob Rees-Mogg has spoken in favour of a Canada-style deal that would keep the Irish Border open.

Committee chairman Hilary Benn said: “It is because the Government has refused to face up to the hard choices confronting us that this deal would represent a huge step into the unknown.

“The Political Declaration falls far short of the ‘detailed and substantive’ document promised by former secretaries of state and by the EU chief negotiator, Michel Barnier.

“It does not give the British people or our businesses the clarity and the certainty they need about our future trading relationship with the EU in five or ten years’ time,” he said.

“And with these negotiations not even having started yet, this could take years to sort out.

“It is now time for colleagues to decide on the Prime Minister’s deal.”

The Sunday Times reported Mrs May was expected to announce on Monday that she was delaying the vote to head to Brussels to make a final appeal to the EU to improve Britain’s exit deal.

However, Brexit minister Stephen Barclay told BBC TV on Sunday: “The vote is on Tuesday, that is what we are focused on.”

“The risk for those who say simply go back and ask again, the risk is that isn’t necessarily a one way street, the French the Spanish and others will turn round, if we seek to reopen the negotiation, and ask for more,” he added.

Mr Barclay said Britain would enter “uncharted waters” if it loses the vote but that Mrs May could stay on as prime minister.

European Union leaders are due to meet in Brussels on Thursday and there has been speculation that Mrs May might use that as a chance to press for changes to a deal that has angered both sides in the debate. – PA, Reuters