Ulster Unionist leader Mike Nesbitt said the likely election would be seen as a referendum on the Democratic Unionist/Sinn Fein-led executive's handling of the RHI scandal

An enraged electorate in Northern Ireland could deliver another Brexit moment and radically reshape the political landscape in the looming snap poll, Ulster Unionist leader Mike Nesbitt has said.

Mr Nesbitt said the likely election would be seen as a referendum on the Democratic Unionist/Sinn Fein-led Stormont executive's handling of a botched renewable energy scandal.

The bold prediction by the leader of the largest Opposition party came after former first minister and DUP leader Arlene Foster claimed a torrent of online abuse aimed at her during the ongoing crisis included one troll threatening to behead her.

Martin McGuinness, who resigned as deputy first minister in protest at Mrs Foster's role in the ill-fated renewable heat incentive (RHI), branded the on-line attackers "cowards", while Northern Ireland Secretary James Brokenshire also condemned the threats.

Northern Ireland will be going to the polls if Sinn Fein refuses to reappoint a deputy first minister to replace Mr McGuinness on Monday - and the republican party has repeatedly made clear it has no such intention.

Mr McGuinness's withdrawal this week forcibly removed Mrs Foster from her role.

In another development on Friday, Sinn Fein Health Minister Michelle O'Neill confirmed the Stormont meltdown meant no steps could be taken in response to an expert panel report examining potential changes to Northern Ireland's strict abortion laws.

Meanwhile, GPs have threatened to resign if a rescue plan to address problems in general practice also falls victim to an executive collapse.

Mr McGuinness's resignation was precipitated by the RHI scandal - a furore that has left Stormont facing a £490 million bill - but the row has since widened to take in a range of unresolved disputes between the region's two ruling parties.

If they are returned as the largest parties again, the likelihood of an immediate return to powersharing is slim and many are predicting a significant period of direct rule from Westminster to enable a major talks process to be convened.

Mr Nesbitt, clearly already in election mode, insisted it was not a foregone conclusion that Sinn Fein and the DUP would be returned to the seat of the executive at Stormont Castle.

While it would be a political shock of seismic proportions if they were not, Mr Nesbitt cautioned people not to rule it out.

Asked if Northern Ireland could experience its own "Brexit moment", he said: "I think if you look at what's happened since the Assembly election last May - you have had a surprise in terms of the referendum on our membership of the EU and you've had a surprise in terms of the American Presidential election.

"Those surprises come when people get angry and people in Northern Ireland are angry about the renewable heat debacle."

He added: "We think this election should be a referendum on the handling of the renewable heat debacle, remembering it is just the latest scandal in a long list over the last 10 years in which the Sinn Fein/DUP coalition have ruled out of the Castle."

The UUP had cooperated with the DUP in previous Westminster elections. Mr Nesbitt refused to be drawn on whether he would rule out further pacts in the future.

Since going into Opposition, Mr Nesbitt and SDLP leader Colum Eastwood have portrayed themselves as an alternative partnership to lead Northern Ireland. However, on Friday, Mr Nesbitt insisted his party would not campaign on a joint ticket with the SDLP.

Earlier, in an interview with the Impartial Reporter, a local paper in her Fermanagh and South Tyrone constituency, Mrs Foster said she had reported online threats against her to the police.

Mr McGuinness said the reported threats were "shameful and totally unacceptable".

"I unreservedly condemn those responsible for the cowards they are," he tweeted.

Mr Brokenshire said they were "completely unacceptable and have no place in our democracy".

Sinn Fein has accused the DUP of "arrogance and disrespect" in office and insisted republicans will only return to government if their long-term coalition partners give way on a series of "equality issues", such as the Irish language and LGBT matters.

The DUP, for its part, has made clear it will not deliver a "republican agenda" and said the very structures of mandatory coalition powersharing need to be reviewed for it to return to Stormont Castle.