THERESA May has been warned that her Brexit transition deal will be voted down in the Commons unless she tears up her "completely unacceptable" proposals for fishing.

Some 14 of the Prime Minister's backbench parliamentary allies - 13 Conservatives and one DUP MP - have signed a joint letter denouncing the draft deal agreed by the UK Government earlier this week.

Mrs May is hoping the transitional agreement will be signed off today at a meeting of EU leaders at the European Council summit in Brussels, clearing the way for crucial talks on post-Brexit trade to begin in earnest.

But the 14 MPs, including leading backbench Brexiteer Jacob Rees-Mogg, said the proposal for Britain effectively to remain in the EU's Common Fisheries Policy for almost two years after Brexit Day in March 2019, with no say over the allocation of quotas, would not command the support of MPs.

"These demands are completely unacceptable and would be rejected by the House of Commons," they declared in a statement.

Two of the Conservative signatories, Aberdeen South's Ross Thomson and Thanet South's Craig Mackinlay, joined Mr Rees-Mogg at the early morning riverside demonstration.

The Somerset MP accused Mrs May of making a “mistake” over the transitional deal, stressing how it was important the rules between Britain’s formal leaving date and the end of the 21-month implementation period did not have an unfair effect on the UK’s fishing communities.

“We hope that things will change. We need to ensure that we have a vibrant fishing community and we want to make sure that it survives to the end of the implementation period to benefit from our being free of the tyranny of the European Union," said Mr Rees-Mogg, who then walked off towards Parliament as the trawler, decked with a Union flag, docked at Westminster Pier.

On board, Nigel Farage, the former Ukip leader, later helped throw fish overboard. The anti-EU MEP said: “They told us they would take back control in 2019; that is not happening. We are now told at the start of 2021 it may happen.

"I don't think this government has got the guts or the strength to stand up and take back our territorial waters."

On Tuesday in a Commons statement, Michael Gove, the Environment Secretary, said he shared the disappointment of fishing communities over the delay in taking back full control of UK waters but he put this down to Brussels’ “intransigence”.

He stressed there were "specific safeguards," which meant Britain would be consulted over the December 2019 quota talks and it had a guarantee that its share would not be reduced.

The Scot warned Brussels if anything was done to harm UK fishing interests during the implementation period, then there would be "unhappy consequences" for others once it became an independent coastal state from December 2020.

Mr Gove,in the face of colleague's criticisms, urged them to “keep their eyes on the prize” of fishing autonomy.

However, the Conservative Government’s opponents have cried foul, saying the promise that Britain would take back control of its waters post Brexit Day had been broken; fishing communities will have to wait almost two years to do so.

Nicola Sturgeon, the First Minister, accused Mrs May and her colleagues of a "massive sell-out".

Meanwhile, Donald Tusk warned there was no guarantee EU leaders would accept the transitional deal later today.

The European Council President pointed out how he still needed more time to consult with "some of the most concerned member states" ahead of their two-day summit.

The leaders of the remaining 27 had been expected to rubber-stamp the transitional arrangements, finalised in the Belgian capital on Monday.

But in his letter formally inviting them to the meeting, Mr Tusk said: "Whether all 27 member states can welcome this at the European Council remains open. I still need a couple more hours to consult with some of the most concerned member states."

A failure to secure agreement on the terms of the UK's withdrawal would be a bitter blow for Mrs May, casting major doubt on her goal of getting broad agreement on Britain's future relationship with the EU, including a free trade deal, by October.

But Downing Street remained sanguine. It insisted "very good progress" had been made.

The PM’s spokesman added: "The European Commission has been clear, as has the European Council, that getting a deal is in the interests of not only the UK but businesses and people across the EU."