Political unionism in Northern Ireland has been thrown into further flux after Ulster Unionist leader Steve Aiken announced his resignation.

Mr Aiken’s move came 10 days after DUP leader Arlene Foster was forced to quit after an internal heave against her.

The announcement from the South Antrim MLA, who will remain as leader until a successor is chosen, was also prompted by mounting discontent within the party over his stewardship.

With Mr Aiken’s decision coming so soon after Mrs Foster’s, unionism is set for a significant realignment ahead of next year’s Assembly election.

The broader unionist and loyalist community in Northern Ireland has been significantly unsettled by the emergence of Brexit’s Irish Sea border and their political representatives acknowledge the election could be pivotal for the pro-Union cause.

And if the political turmoil ends up destablising the powersharing administration in Belfast, the election could come sooner than scheduled.

Mr Aiken, a former submarine captain, was elected UUP leader unopposed in 2019.

Many are tipping Upper Bann MLA Doug Beattie as a likely successor.

In a letter to party chairman Danny Kennedy, Mr Aiken said he believed he had taken the party as far as he could.

“To achieve our goals, we now need new leadership,” he wrote.

Mr Aiken said he will remain in politics and continue as a South Antrim MLA.

Discussing his time as leader, Mr Aiken said he took pride in the party’s decision to take on the challenging health minister portfolio when Stormont was restored in 2020.

He said his party colleague and former leader Robin Swann had been successful in his efforts to tackle the pandemic.

“However, despite our successes, it has become clear to me that if we are to achieve the breakthrough in the forthcoming Assembly elections, we will need to drive further ahead,” Mr Aiken wrote to the party chairman.

“To represent the brand of unionism that builds on hope and not fear, and provides a clear, modern, alternative that will be both the future of our party and Northern Ireland, will require strong leadership.”

He insisted unionism needed positive, hopeful and progressive leadership.

“The last few months have been a momentous time for our Union and for Northern Ireland,” he wrote.

“It is also a time when unionism, more than ever, needs positive, hopeful and progressive leadership; leadership which I strongly believe only the Ulster Unionist Party can provide.

“Our party has delivered for the people of Northern Ireland for many years and in the centenary of Northern Ireland continues to do what is right – not just for unionists, but for everyone.”

In a written reply to Mr Aiken, party chairman Mr Kennedy said he “regretfully” acknowledged his decision to resign.

“On behalf of the officers and the entire party I want to express my deep appreciation for the service you have rendered as leader and pay tribute to your unstinting efforts to promote our raison d’etre – the maintenance and preservation of Northern Ireland’s place in the United Kingdom,” he wrote.

Mr Beattie was among those paying tribute to the party leader.

“The loneliness of leadership is never easy,” he tweeted.

“The cruel comments are a measure of those unwilling to put their heads above the parapet.

“As my party leader, my colleague and my friend I want to thank Steve for his for service past, present and in the future.”

Mr Swann tweeted: “I want to thank @SteveAikenUUP for his leadership, it is oft time both a rewarding and challenging position to hold.

“But most of all I thank him for his support and the trust he placed in me when he nominated me as Health Minister.”