Three of Northern Ireland's main political parties have written a joint letter to British Prime Minister Boris Johnson rejecting his plan for unilateral legislation on the protocol.

It was signed by MLAs from Sinn Féin, Alliance and the SDLP.

In it they said they "rejected in the strongest possible terms your government's new reckless protocol legislation".

They said it flew in the face of the wishes of most businesses and the majority of people in Northern Ireland.

Whilst the protocol was not ideal, they said it was the best option to protect Northern Ireland from the worst excesses of a hard Brexit.

They rejected the UK government claim that its intention was to protect the Good Friday Agreement.

"To complain the protocol lacks cross-community consent, while ignoring the fact that Brexit itself – let alone hard Brexit - lacks even basic majority consent here, is a grotesque act of political distortion," they wrote.

"Your claims to be acting to protect our institutions is as much a fabrication as the Brexit campaign claims you made in 2016."

The three parties said they collectively represented a majority at the Northern Ireland Assembly and a majority of the votes cast in the recent assembly election.

They said the way to fix the issues with the protocol was to engage properly with the EU to find a negotiated settlement.

"We will resolutely oppose this reckless Bill and continue to promote post-Brexit solutions on the basis of trust and honesty," they concluded.

Sinn Féin Stormont leader Michelle O'Neill is among the signatories.

In a tweet she described the "unilateral actions of Boris Johnson" as "utterly reckless".

"It is clearly a breach of international law. The impact on our businesses and economy could be colossal," she tweeted.

"The pro-protocol parties have jointly written to Boris Johnson today to firmly reject his legislation and approach."

Ms O'Neill said Northern Secretary Brandon Lewis was "talking nonsense" when he said the legislation would not breach international law.

"The majority of people want the protocol to work, it's the best defence against the hardest possible Brexit," she said.

"The majority of businesses are saying the protocol is working and affording them opportunities.

"We want to see more of that but all Boris Johnson is doing today is furthering political instability and creating economic uncertainty in the days and weeks ahead."

The Democratic Unionist Party blocked the formation of a new power-sharing government at Stormont following last month's Assembly election in protest at the protocol.

DUP leader Jeffrey Donaldson welcomed the move on legislation.

He said finally he was seeing "the kind of action that is required" to begin the process of removing barriers to trade within the UK and restoring Northern Ireland's place within the internal market.

He said he would consider the bill with interest.

"We want to see the bill progressing in parliament, publishing the bill doesn't deliver anything in and of itself but it is nonetheless an important step and we recognise that," he said.

"As the bill progresses we will then consider what that means for devolution in Northern Ireland."

Senior DUP politician Sammy Wilson has said the party will only move to restore Stormont if it is sure British government plans to override post-Brexit trade rules will become law.

"If this bill has a tempestuous process through the House of Commons, amendment after amendment, attempts to weaken it, it's likely it will face the same in the House of Lords, our assessment would be it would be very foolish to make any commitment to go back into the Assembly."

Analysis

Jeffrey Donaldson will undoubtedly be under pressure to deliver some kind of quid pro quo in return for the introduction of the legislation.

But the DUP is unlikely to be in any hurry to do so.

He chose his words very carefully today: welcoming what he described as an important step, while at the same time signalling that more steps are required.

The Lagan Valley MP spoke of a desire to restore the political institutions at Stormont without giving any commitment to do so.

The aim of this legislation is to persuade the DUP to go back into power sharing, while also trying to wring more concessions from the EU.

Mr Donaldson described the move as a step towards dealing with the problems he says the protocol has caused, and restoring Northern Ireland's economic and constitutional integrity within the UK.

But he was careful to add caveats, stating that "publishing the Bill doesn't deliver anything in itself".

The DUP leader said his party will give it careful consideration, but stressed that it wants to see "where the Bill is going."

His party will monitor the legislation’s progress through Parliament to ensure that the final Bill "delivers what is required."

DUP leader Jeffrey Donaldson speaks to the media in the Great Hall at Stormont today

Asked whether the contents are sufficient for his party to reciprocate by agreeing to the appointment of a Speaker at Stormont - which would allow the Assembly to function - he said it will weigh it against seven tests the party has set.

The replies reflect the fact that the DUP, like the Irish Government and EU, does not trust Boris Johnson.

The first reading if the Bill is just the first step in a long journey that will see it pass through acrimonious debates in the House of Commons and then well signalled opposition in the House of Lords.

During that time there will be amendments and adjustments and the final version might not be as palatable to the DUP as this initial draft.

Senior DUP sources have suggested in recent weeks that the party will not pass final judgement until the Bill receives Royal Assent and enters the statue books, a process that could take a year or more.

It will come under intense pressure to make some reciprocal moves well before then, but sources suggest that is unlikely to happen in the short term.

Whatever merits the DUP may see in this proposed legislation, there’s also Northern Ireland’s traditional Twelfth marching season to consider.

The party will be wary of any perceived concession on its part that could be seized upon by unionist and loyalist critics as a sign of weakness at a time when political and sectarian divisions are heightened.

As far as it’s concerned, the stronger and louder the criticism of its stance from the Irish government and Sinn Féin, the better.