Sir Jeffrey Donaldson has denied there is any agreement between the DUP and the Government to bring back double-jobbing for politicians in Northern Ireland.
But amid a deepening political row over Government proposals for dual mandates, Ulster Unionist party leader Doug Beattie claimed Secretary of State Brandon Lewis had previously told him the plan would not go ahead as it did not have cross-party support.
Sinn Fein deputy First Minister Michelle O’Neill accused the UK Government of interfering in the Northern Ireland Assembly election to prop up the DUP.
Four of the five parties that make up the Executive in Stormont have come out against the plans by the Northern Ireland Office.
The DUP leader has confirmed his intention to seek the dual positions of MLA and MP, but has refused to say if any of his party colleagues will do the same.
The return of the “dual mandate”, or double-jobbing, would allow the DUP leader to contest the forthcoming Assembly elections while also remaining MP for Lagan Valley at Westminster.
The current law banning politicians from double-jobbing as MLAs and MPs came into effect in 2016.
It is understood that the new transitional arrangements being considered by the Government would be on a recurring basis, to avoid the need for triggering by-elections.
This means that a sitting MP who became an MLA would then have to stand down from their Westminster seat at the next general election.
However, the same arrangements could be used in future elections for politicians who wanted to transfer from Westminster to Stormont.
Similar arrangements already operate in other parts of the UK.
I take with a pinch of salt some of the outrage we're now seeing manifested by some of the political partiesSir Jeffrey Donaldson
Speaking on Monday, Sir Jeffrey said: “Let me be absolutely clear – there is no agreement between the Government and the DUP on this.
“This issue was first raised by the Labour Party back before I became leader of the DUP.
“We then had, before Christmas, a debate in the House of Lords on this issue; again, not something that was initiated by the DUP.
“And there was no opposition at that stage to what was being put forward.”
The DUP leader added: “So I take with a pinch of salt some of the outrage we’re now seeing manifested by some of the political parties.
“I’m talking about dual mandates, because, in the end, as I declared when I was elected leader, I made clear I wanted to contest the Assembly elections.
“In the autumn I put my name forward for selection within the party; that process is ongoing. But if I’m selected, then I will put myself before the people in Lagan Valley.
“Ultimately, they will decide whether they want their MP to also be an MLA and that is called democracy.”
Sir Jeffrey denied the arrangement would just benefit the DUP and said any MP could avail of it.
He added: “It is not there for the long term and, if someone is elected in mid-term as an MP, elected to their local assembly, then they can opt to remain an MP until the next general election.
“And that actually brings Northern Ireland into line with other parts of the UK.
“And, as I say, it is a transitional arrangement. It’s not intended to ensure that dual mandates continue indefinitely in those circumstances.
“I believe there is a case to be made, and I will make the case to the people of my constituency that, as DUP leader, I think it is important that my voice continues to be heard at Westminster.”
Amid reports that a second DUP MP is seeking to secure a Stormont seat, Sir Jeffrey refused to confirm whether any of his party colleagues have put their names forward for the Assembly elections later this year.
Speaking to the BBC, he said: “The bulk of DUP MPs have not put their name forward for selection.
“I see some parties saying that all eight DUP MPs will be standing in the Assembly elections – that simply is not true.”
Ms O’Neill accused the UK Government of rewarding the DUP.
She said: “They’re interfering to serve only the DUP. They are interfering to prop up the DUP in the election campaign. This is the very same DUP that are threatening the stability of politics.
“They’re threatening to walk away from the institutions from last September.
“And, whilst the rest of us are turning their face towards dealing with the pandemic, tackling violence against women and girls, dealing with health waiting lists, the DUP are constantly threatening to pull down our politics here.
“The British Government have rewarded them over the weekend by propping them up in terms of giving Jeffrey Donaldson an each-way bet.”
Mr Beattie said: “Here we are on the cusp of an Assembly election and somebody has moved the goalposts.
“They have given a leg up to one political party and not to any other political party.
“And, let’s be absolutely clear – I sat in front of the Secretary of State (Brandon Lewis) and other members of the Northern Ireland Office, and I asked about the amendments that were going through in regards to this Bill.
I think that it is a scam. I think it's a subversion of our democracy. I think it's wrongUUP leader Doug Beattie
“And what the Secretary of State said to me was there isn’t party consensus for such an amendment, so therefore they would not be taking it forward.
“Yet here we are, an amendment that has been put forward, which has not got party consensus, and will only benefit the DUP, and the NIO are allowing it to go through.
“I think that it is a scam. I think it’s a subversion of our democracy. I think it’s wrong.”
A spokesman for the Northern Ireland Office confirmed at the weekend that the Government had tabled an amendment to the Northern Ireland (Ministers, Elections and Petitions of Concern) Bill and said it would be subject to the usual parliamentary scrutiny.