Boris Johnson – Andrew Parsons/ No10 Downing Street

Boris Johnson’s trade deal has passed the “acid test” set by the most hardline Tory Eurosceptics as they confirmed they will vote for it in Parliament on Wednesday.

The European Research Group (ERG) said that while the deal was not “perfect”, it fulfilled the requirement of guaranteeing sovereignty for Britain as an independent nation.

The ERG convened a “Star Chamber” of Eurosceptic lawyers, chaired by veteran campaigner Sir Bill Cash MP, which gave its blessing to the deal after scrutinising the 1,246-page document.

Writing in today’s Telegraph, Mark Francois, the chairman of the ERG, says the deal “unambiguously” passes the test of preserving the UK’s sovereignty “as a matter of law”.

Mr Francois was one of the 28 Tory “Spartans” who held out against former Prime Minister Theresa May’s original Withdrawal Agreement, helping to bring about her downfall as she was unable to get the legislation through Parliament.

He describes the deal as “a massive victory” for Lord Frost and the UK negotiating team and a “personal triumph” for the Prime Minister, who has carried out his promise to “Get Brexit Done”.

In its assessment of the deal, the ERG’s legal advisory committee said that it was “sovereignty compliant” because it contains no role for the European Court of Justice and establishes an “independent arbitrator” for any future disputes.

It therefore “fully respects the norms of international sovereign-to-sovereign treaties”.

It also highlights the fact that the UK can terminate the deal with 12 months’ notice in future if it decides to do so.

However, the ERG lawyers warn that the Government must be “robust” in ensuring that it does not get pushed around by Brussels in relation to “level playing field” agreements.

They are happy with the UK’s agreement on “non regression” clauses that require the UK to maintain current standards and regulations on goods, employment law and other matters, as Britain still has a right to diverge, if it wishes, subject to the risk of tariffs being imposed as a part of a “rebalancing mechanism” to ensure fair competition.

In a statement, the “Star Chamber” said: “We think that as long as a UK Government is willing to be robust and to defend with vigour any arbitration proceedings launched by the EU, then the rebalancing mechanism is less likely to give rise to a serious, effective constraint on practical UK sovereignty to revise our own laws in these fields.”

Theresa Villiers, the former Cabinet minister and committed Brexiteer, said: “I will vote for Boris’s deal. Having studied it, I believe that it will enable us to take back control of our laws, our money and our borders.

“Some of the compromises are difficult but this free trade agreement will get Brexit done.

“It’s been a long and difficult road, but we are now on the brink of becoming an independent country once again.”

The ERG’s lawyers pointed out that the deal “temporarily limits the exercise of the UK’s sovereign rights over its waters that would apply in the absence of the agreement”, but accepted that some compromise was necessary and that after a five and a half year fishing transition period the UK “will have the legal right to take full control of its waters”.