The leader of the DUP has hit back at accusations the party is not opposed to the Northern Ireland Protocol.

Sir Jeffrey Donaldson said its “political critics” were claiming the DUP is not against the controversial protocol.

In a letter to party members, seen by the PA news agency, Sir Jeffrey said that its political unionist opponents need to “wise up”.

The letter comes hours after senior DUP MP Sammy Wilson was loudly booed and jeered as he addressed a loyalist rally against the Northern Ireland Protocol.

Mr Wilson was repeatedly interrupted as he attempted to deliver a speech at the event at Markethill in Co Armagh on Friday.

During his address, Mr Wilson compared the EU’s handling of Northern Ireland in the Brexit process with Vladimir Putin’s annexation of Crimea in Ukraine.

However, his comments were often drowned out as angry crowd members accused his party of botching the Brexit process.

Thousands of people attended the rally, with dozens of bands from across Northern Ireland taking part.

Jim Allister and Sammy WilsonTUV leader Jim Allister (left) intervenes during a speech by DUP MP Sammy Wilson at an anti-NI Protocol rally in Markethill, Co Armagh to appeal to the crowds to stop booing him (Cate McCurry/PA)

At one point in Mr Wilson’s speech, Traditional Unionist Voice leader Jim Allister intervened and appealed to those in attendance to hear him out.

On Saturday, Sir Jeffrey said in a letter: “Some of our political critics are attempting to claim the DUP is not opposed to the Northern Ireland Protocol.

“At a time when I am trying to encourage greater unity in opposition to the protocol, they are seeking to undermine such unity for purely party political reasons.

“They need to wise up and recognise that our strength is in our unity.

“We have taken decisive action in our opposition to the protocol.

“It is the actions of this party in withdrawing ministers from the North South Ministerial Council, in challenging and attempting to frustrate the checks at ports and ultimately in the resignation of the First Minister, that has highlighted that the protocol is not compatible with stable local arrangements.

“It is this party that has made clear that if the long shadow of the Northern Ireland Protocol is not removed from Stormont then we will not have the stable basis, supported by both unionists and nationalists, to form an Executive.”

On Saturday, Mr Wilson accused Mr Allister of “whipping up an anti-DUP sentiment”.

He said that some in loyalism are intent on “manufacturing disunity where none exists”, and that it undermined the message of the rally.

“Whilst Jim Allister appealed for respect, it came after he spent then minutes on the platform whipping up an anti-DUP sentiment in a blatant act of electioneering,” Mr Wilson said.

“Whilst Sir Jeffrey has sought to work with every hue of unionism, whether he always agrees with them or not, to get a united front and common cause against the protocol, it seems Jim is only interested in using the protocol to promote his and his party’s narrow electoral interests.

“Unionism is ill-served at this time by such division.

“Regardless of how some may try to hijack opposition to the protocol, the DUP will focus on harnessing all unionist energies to ensure the protocol is removed.

“Does Jim want a united opposition to the protocol or not? Does he see these rallies as an opportunity to present a united front or simply to attack others sharing the platform with him?”

Responding to Mr Wilson’s comments, the TUV leader said his party is “not responsible” for the public perception of the DUP on Brexit issues.

“If Sammy Wilson thinks unwarranted personal attacks on me helps his party’s cause, that is a matter for him and the DUP,” Mr Allister said in a statement.

“How such helps the stance against the protocol is difficult to discern.

“TUV is not responsible for the public perception of DUP’s protocol stance, especially after foolish talk about ‘the best of both worlds’.

“The public has no problem understanding TUV’s unwavering stand against the Union-dismantling protocol.”

The protocol has created new economic barriers on trade between Northern Ireland and the rest of the UK.

Agreed by the UK and EU to ensure no hardening of the Irish land border post-Brexit, it has instead moved regulatory and customs checks to the Irish Sea, with Northern Ireland remaining in the EU single market for goods. The region also applies the EU customs code at its ports.

Unionists and loyalists claim the arrangements have undermined the sovereignty of the UK, but a majority of Assembly members at Stormont support the protocol, claiming it offers Northern Ireland a degree of protection from negative economic consequences of Brexit.

The EU and UK continue to negotiate in a bid to agree a way to reduce the bureaucracy associated with the protocol.

“When I addressed party members on Thursday February 3 on the announcement of the resignation of the First Minister I said that if the protocol is left in place, then the divergence between Northern Ireland and the rest of the United Kingdom will grow and without a single vote cast, the protocol will have re-oriented our supply chains and our economy away from Great Britain,” Sir Jeffrey added.

“Laws will be made and implemented that impact every citizen without any local representative having shaped them or voted upon them.

“There comes a moment when we have to take tough decisions if we are to build for the future.

“While others talk about what they will do, the DUP took action.”