Former prime minister Boris Johnson has said he is going to vote against Rishi Sunak’s new Brexit deal for Northern Ireland.

The Windsor Framework was agreed by the prime minister and European Commission President Ursula von der Leyen on 27 February to change the way the Northern Ireland Protocol operates.

A crunch vote on the key part of the legislation will take place on Wednesday afternoon, when MPs will decide whether they want to back the Stormont brake or not.

Mr Johnson said the proposed new arrangements would mean the “whole of the UK” was unable “properly to diverge and take advantage of Brexit”.

“The proposed arrangements would mean either that Northern Ireland remained captured by the EU legal order – and was increasingly divergent from the rest of the UK – or they would mean that the whole of the UK was unable properly to diverge and take advantage of Brexit,” he said.

“That is not acceptable. I will be voting against the proposed arrangements today.

“Instead, the best course of action is to proceed with the Northern Ireland Protocol Bill, and make sure that we take back control.”

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The Northern Ireland Protocol was agreed by Mr Johnson as part of his “oven ready” Brexit deal to prevent a hardening of the land border on the island of Ireland – which all sides agreed was necessary to preserve peace.

But it led to trade barriers being created between Great Britain and NI, effectively creating a customs border down the Irish sea – something the former prime minister promised would not happen.

As a result Mr Johnson sought to pass the Northern Ireland Protocol Bill – a controversial piece of legislation aimed at overriding parts of the UK’s Brexit withdrawal agreement with the EU.

The move soured relations with Brussels, who said it would breach international law, and Mr Sunak paused the bill while attempting to negotiate a new deal after taking office.

The Windsor Framework aims to reduce red tape on goods passing between Northern Ireland and the rest of the UK by implementing a green and red lane system, while addressing the so-called “democratic deficit” unionists said had arisen from the protocol arrangements through the Stormont brake.

This mechanism would allow a minority of politicians in Belfast to formally flag concerns about the imposition of new EU laws in Northern Ireland – a move that could see the UK Government veto their introduction in the region.