Northern Ireland Protocol and Windsor Framework: TUV leader Jim Allister confirms his party members put controversial poster outside DUP leader Sir Jeffrey Donaldson's office

Sir Jeffrey posted a photo of the poster which read Stop DUP sell out on social media.

The poster read "Stop DUP sell out" but did not identify who had produced it.

It is understood the same poster has been placed at different locations across Northern Ireland.

The posters have been erected as speculation mounts that the DUP is set to strike a deal to return to powersharing at Stormont.

The party walked out 22 months ago in protest at the commercial and constitutional impact of the Northern Ireland Protocol on the union with Britain.

"This is a poster erected by TUV members captured on CCTV last night outside my constituency office," Sir Jeffrey said on Sunday night.

"Like cowards they arrived in the middle of the night and tried in vain to hide their identity but they are known to us.

"I will not be intimidated or distracted by such shadowy behaviour any more than similar behaviour I have faced in the past by republicans.

"So much for the TUV wanting unionists to stand together. Their mission is to divide, vote split and undermine their fellow unionists. They were rejected in Lagan Valley in all recent elections. In contrast, I have a strong mandate to negotiate the restoration of our place in the UK and its internal market. I will continue in that task until I have made the progress needed to protect our place in the Union and restore Stormont. These cowards will not deter me from doing my job."

Mr Allister said in response today that the posters "were a message to the DUP".

"I had knowledge that the posters were being printed, I had no idea where or anything else and I know that TUV members were involved and I know that they were involved because we are in touch with the grass roots," he told the BBC.

He said unionist grass roots were "concerned about being sold out again and that the protocol will not be removed".Mr Allister described the posters as "a bit of political activism to which there's been a huge overreaction".

The TUV also issued a fuller statement today confirming that party members were involved in putting the posters up.

It said: “The fundamentals are these - is the Protocol to stay? Is EU law to stay? Is the Irish Sea Border to remain? If the answer to those questions is yes then there is no deal on the table which is acceptable to Unionists who remain true to our solemn pledges to the people in the united Unionist declaration and only those prepared to sell out would argue otherwise.

“TUV members were involved in the erection of the posters but this is much bigger than that. This is the product of a sense within grassroots Unionism that they are being ignored. Political commentators the media elite have been telling them that any settlement isn’t going to remove the Protocol and this was a response to say that any settlement of that nature would be a sell out. There is a fear in Unionism of a sell out. Denial of that is a denial of reality.

“TUV believe these posters are a message to the DUP to stand true to their pledges to the Unionist people and indeed present the DUP with an opportunity to tell the Government that the Unionist discontent hasn’t gone away and won’t be bought off by bribery or blackmail.

“I imagine anyone who put up the posters would be delighted to be proved wrong by a deal which sees the Protocol gone, EU law gone, the Sea Border gone, Article Six of the Acts of Union restored and Northern Ireland back as a full and equal part of the UK.

“As for claims that the posters are intimidatory one does have to question if the DUP are the people to be negotiating on behalf of Unionism with a difficult UK Government if that is really how they feel about a few bits of corex. A lot more bottle than that is required if a deal is to be secured which will be acceptable to Unionism.

“The grassroots are saying we have had enough. We were promised in the joint Unionist declaration opposition to the Protocol was the “unalterable” position of all Unionists. If position has changed for some now that elections are out of the way then that is sell out.”