Pro-Irish unity party Sinn Fein has become Northern Ireland's largest party in London for the first time, holding its seven parliamentary seats while the largest pro-UK party lost three of its eight.

Sinn Fein, formerly the political wing of the paramilitary IRA during the British region's long-running conflict known as the "Troubles", is also the largest party at council level and at the devolved Northern Ireland assembly.

Newly elected Sinn Fein MPs -- who abstain from taking up their seats in the UK parliament because they do not recognise British sovereignty over Northern Ireland, include former UK midwives' union head Pat Cullen.

During the campaign the DUP (Democratic Unionist Party) had to fend off criticism from pro-UK loyalists over a deal with London that ended the party's two-year-long boycott of the devolved assembly over post-Brexit trading rules.

Critics portrayed the deal last February as undermining Northern Ireland's place in the UK by maintaining checks on goods arriving in the province from the mainland that they said amount to a "sea border".

In several constituencies the pro-UK unionist vote share was split between two or more candidates.

In an upset, Jim Allister, one of the fiercest critics of the DUP's deal, won a seat held by the DUP's Ian Paisley whose father -- also Ian -- was a Protestant religious leader and militant pro-UK loyalist during the Troubles before later becoming Northern Ireland's First Minister.

The DUP also had to quickly appoint a new leader, Gavin Robinson, after the shock departure of former head Jeffrey Donaldson following his arrest and charging over alleged historical sex offences in March.

Robinson narrowly held his Belfast seat ahead of Naomi Long who leads the cross-community Alliance party.

AFP

Sinn Fein Party vice president Michelle O'Neill walks at the Stormont Parliament Buildings on the day Northern Ireland lawmakers elect the Irish First Minister, in Belfast, Northern Ireland, February 3, 2024. REUTERS/Suzanne Plunkett/File Photo

Sinn Fein becomes largest NIreland party in Westminster