The European Union is demanding it retain control of Britain’s ravaged fisheries as the price of approving Theresa May’s plan to keep the country in the EU Customs Union, according to reports.

The Prime Minister’s proposals for Britain to duplicate EU rules and regulations through a ‘common rulebook’ managed by EU judges and to remain within the bloc’s Customs Union — effectively preventing the country from reestablishing an independent trade policy — were originally seen as heavy concessions, but there is now a sense in Westminster that entering into such an arrangement would be some sort of victory, as Brussels has been resisting it.

The whole scheme is seen as necessary in order to maintain the supposedly all-important customs-free border between the Republic of Ireland and the British province of Northern Ireland after Brexit.

Eurocrats have been demanding that Northern Ireland alone be kept within their Customs Union and Single Market — economically annexing the Province and erecting an economic barrier between the United Kingdom’s Home Nations — with Theresa May’s offer to keep the entire country in the Customs Union as an alternative falling on deaf ears.

It is now understood that Brussels may be willing to accept May’s Brexit in name only deal — provided she agree that Britain will continue to surrender its fishing waters to EU fishermen, who currently claim more than half of the island nation’s stocks, with disastrous effects for British industry.

Fishing is the acid test of Brexit, we must take back our waters from Brussels. pic.twitter.com/ekQt6RppJe — Nigel Farage (@Nigel_Farage) November 9, 2018

“If Mrs May and her sycophantic Cabinet and MPs cave into this demand then they will be slaughtered in constituencies nationwide,” warned Fishing for Leave, the exasperated grassroots fishermen’s campaign which organised the (in)famous Battle of the Thames protest during the 2016 referendum.

“Given her current supine performance to date we see nothing to suggest she and her government won’t,” they added.

“The EU is now ‘cherry picking’… it is how weak the government has been that has encouraged the EU to think they can rub Britain’s nose in the mud over this totemic issue,” the group complained.

Not even Norway and Iceland, the two coastal members of the European Economic Area (EEA), are expected to give up their fisheries as the price of free trade with the European Union.

Nor have similar demands been made of Turkey, which is incorporated into the bloc’s Customs Union with respect to industrial goods.

“[Theresa May] has another thing coming if she thinks British fishermen and coastal communities are going to lie down to a second sell-out that will finish most of us,” Fishing for Leave added.

“Norway, Iceland, Faroe [and] Greenland export vast amounts of seafood to the EU. Does the EU demand and do they cave to surrendering their natural resource for market access? NO.

“No other nation on earth gives up fisheries access and resources for markets… looks like the Conservatives are about to make Britain the first.”

The PM’s letter raises alarm bells for those who value the integrity of our precious union & for those who want a proper Brexit for the whole UK. From her letter, it appears the PM is wedded to the idea of a border down the Irish Sea with NI in the EU SM regulatory regime. https://t.co/qN6c41zx7U — Arlene Foster (@DUPleader) November 9, 2018

The fishing revelations come as Northern Ireland’s Brexit-supporting Democratic Unionist Party (DUP), on which Theresa May’s minority government relies for a parliamentary majority, says they are concerned the Prime Minister intends to renege on her promise that she will not sign off any deal which could risk a customs border between Ulster and Great Britain “in the Irish Sea”.

A leaked letter from the Tory leader to DUP leaders indicates that, even if her whole-UK plan for continued Customs Union membership is agreed as a ‘backstop’ solution to the Irish border issue, the EU is still pushing for a so-called ‘backstop to the backstop’ which would keep the Province under its sway alone if talks between the UK and EU collapse.

Mrs May tells the DUP she would never allow such an agreement to “come into force” — but this has been interpreted as meaning she will agree to it in principle.

“The PM’s letter raises alarm bells for those who value the integrity of our precious union and for those who want a proper Brexit from the whole UK,” warned DUP leader Arlene Foster. “From her letter it appears the PM is wedded to the idea of a border down the Irish Sea with [Northern Ireland] in the EU [Single Market] regulatory regime.”

Follow Jack Montgomery on Twitter: @JackBMontgomery