A plan by the UK government to temporarily restore double-jobbing for Northern Irish politicians has triggered fierce opposition from some political parties.

The UK government is facing criticism over plans to allow MPs to retain their seats in Westminster while being elected to the Northern Ireland Assembly.

The return of the "dual mandate", or double-jobbing, would allow DUP leader Jeffrey Donaldson to contest the upcoming Assembly elections while also remaining as the MP for Lagan Valley at Westminster.

Today, the leader of the Ulster Unionist Party, Doug Beattie, accused the Northern Ireland Office of effectively supporting the DUP election campaign.

The details of the move are outlined in a letter from Northern Ireland Office junior minister Jonathan Caine to members of the House of Lords.

It would see dual mandates returning only until the next UK general election in 2024.

The current law banning politicians from double-jobbing as MLAs and MPs came into effect in 2016.

The letter, seen by PA news agency, says that the aim of the rule-change is to avoid triggering by-elections in Northern Ireland.

In the letter, Mr Caine said: "There is no appetite or consensus in Northern Ireland to allow dual mandates to continue indefinitely or to return to a situation in which the overwhelming majority of MPs from Northern Ireland were also members of the Assembly."

He told peers that the "objective" of the UK government is to support the functioning of the Assembly by "providing stability in instances where the Northern Ireland parties need to reconfigure their representation across parliament and Stormont, without the triggering of parliamentary by-elections".

The UK government, Mr Caine said, plans to submit an amendment to change the law on dual mandates in the coming weeks.

It is part of a raft of measures, already passed through the House of Commons, designed to consolidate power-sharing in Northern Ireland following the return of the Executive in early 2020.

However, the plans to restore the dual mandate have already proved controversial and have been criticised by some parties in Northern Ireland.

There had been intense speculation in political circles about how and when Mr Donaldson would return to local politics in Northern Ireland as an MLA, following his election as leader of the party.

He had pledged to return to the Northern Ireland Assembly, after being elected as DUP leader last summer.

It comes as the new party leader grapples with unionist anger at controversial post-Brexit arrangements for Northern Ireland, as well as concerns about slipping poll ratings for the DUP following months of internal divisions.

The DUP share of the vote in Mr Donaldson's constituency was also slashed by over 16% in the 2019 general election, making a by-election in Lagan Valley an unappetising prospect for the party.

Mr Beattie tweeted: "The fact NIO now directly supporting DUP election campaign means they are not a neutral department."

Sinn Féin's deputy leader Michelle O'Neill said on Twitter: "The Tories reversing the ban on double-jobbing to prop-up the DUP is a blatant and disgraceful interference in the Assembly election."

Alliance Party leader Naomi Long called it a "seriously retrograde step".

She tweeted: "I staked my own political future on ending double jobbing in 2010, when I left Council and the Assembly to focus on representing my constituents in Westminster. I was successful in getting double jobbing banned.

"Other parties promised to act but only did when forced by legislation in 2014.

"I've been both an MP and an MLA: you cannot properly do both jobs in the long term.

"The ban was subject to extensive consultation: this reversal has not been.

"Fairly obvious why it's being done."

Leader of the Traditional Unionist Voice (TUV) Jim Allister called the plan a "shameless fix".

"Last throw of the dice for some," he tweeted.

"Dual mandates were abolished for good reason. That reason hasn't changed. Only the desperation of the DUP has changed. What price has the DUP paid for this?"