The leaders of the UUP, SDLP and Sinn Fein have issued statements of congratulation to Jeremy Corbyn after he seized victory in the Labour leadership contest.
Mr Corbyn is drawing up a new-look Labour frontbench team after his seismic victory in the party’s leadership race sparked a flurry of senior resignations.
The veteran left-winger won a landslide victory with almost 60 per cent of the vote - trouncing mainstream rivals Andy Burnham, Yvette Cooper and Liz Kendall.
Ulster Unionist leader Mike Nesbitt MLA congratulated him and added: “I trust Mr Corbyn will do nothing by way of altering Labour’s policy on Northern Ireland, and will affirm he will support agreements brought forward by the local parties here in Northern Ireland.
“I also hope he takes an early opportunity to back the current Shadow Secretary of State, Ivan Lewis MP, in the call he made last week, identifying mental health and wellbeing as an area where Northern Ireland deserves additional, ring-fenced, hypothecated funding from London.”
SDLP leader Dr Alasdair McDonnell said: “Jeremy and his deputy leader Tom Watson have a major task ahead of them to return the Labour Party to an electable position after the General Election but it is critical that the disastrous Conservative ideologies are challenged by every party across these islands.
“We in the SDLP will continue to do that and urge Labour to stand with us and other parties in Westminster.”
The Sinn Fein leader Gerry Adams said: “I have known Jeremy for many years.
“He is a good friend of Ireland and of the Irish peace process.
“I wish him well in his new and challenging role as leader of the British Labour Party and look forward to working with him in the time ahead to ensure that the gains of the peace process are built upon.”
Mr Corbyn topped the ballot not just among new supporters paying £3 to join and trade unionists but also full party members, making it extremely difficult for any disgruntled moderates to mount a bid to unseat him before the 2020 general election.
In an acceptance speech to cheering supporters at Westminster, he called repeatedly for “unity” and announced his ambition to lead a Labour “fightback”.
But the scale of his task in bringing the party together around a radical programme was underlined by the immediate departure of several frontbenchers.
Ms Cooper was joined by Rachel Reeves, Emma Reynolds and Jamie Reed in announcing they would not serve on the frontbench while Ms Kendall, Tristram Hunt and Chris Leslie had already indicated their political differences with Mr Corbyn.
Ed Miliband - whose resignation after leading the party to general election disaster in May provoked the contest - called on the party to join him in supporting Mr Corbyn but indicated that he too would not seek a return to the frontline.
However, shadow business secretary Chuka Umunna - a senior centrist who withdrew from the contest after a matter of days - issued a plea for the party to “come together” behind its new leader “ and focus on providing the most credible and effective opposition to the Tories”.
Corbyn supporters chanted “Jez we did” and sang the socialist anthem The Red Flag as they celebrated his comprehensive victory, taking 59.5 per cent of the vote - 251,417 of the 422,664 votes cast - against 19 per cent for Mr Burnham, 17 per cent for Ms Cooper and 4.5 per cent for Ms Kendall.
The new leader has spent his entire 32-year parliamentary career on the backbenches and entered the leadership contest as a 200-1 outsider before generating a wave of enthusiasm which swept him to victory.
He sought to galvanise that support first in a victory party with activists at a Westminster pub and then by addressing - as his first official engagement as Opposition leader - a huge crowd attending a pro-refugee rally in Parliament Square.
Now, he is familiarising himself with the party’s nearby HQ as he starts to piece together a shadow cabinet able to deliver his anti-austerity, anti-war policies without splitting the party.
Union leaders welcomed his victory but Conservative Defence Secretary Michael Fallon said a Corbyn-led Labour posed “a serious risk to our nation’s security, our economy’s security and your family’s security”.
West Bromwich East MP Tom Watson was elected deputy leader and is expected to play an important role in helping to build Mr Corbyn’s frontbench team and maintain party unity and discipline.
Mr Corbyn admitted he was “a bit surprised” at the scale of his majority, which he said amounted to a “fantastic mandate for change in British politics, with a fantastic enthusiasm for real democratic politics”.
Asked whether he now faces a challenge to construct a shadow cabinet without several senior figures who have said they will not join, the new Labour leader said: “There’s going to be an inclusive, open process.
“I hope everyone will recognise the mandate we’ve received and that party members expect our party to deliver for them in Parliament.”