Michael Matheson has been urged to resign for his role in a "bullying" row involving the SNP's general election candidate in Falkirk.

The Herald on Sunday understands that the entire Westminster Campaign Committee (WC) for the constituency is on the brink of quitting over the bitter feud involving the beleaguered Health Secretary.

Toni Giugliano was selected to be the candidate for the seat at the end of October, following a ballot of local members.

Mr Matheson backed one of his rivals.

READ MORE: Probe into Matheson's £11k data bill won't report until New Year

Following Mr Giugliano’s selection, a complaint was made to SNP HQ about his campaign.

He was accused of placing undue pressure on local members to support him, fabricating an endorsement, breaching spending limits in the internal contest and then lying about it.

Mr Giugliano has rejected all of the allegations.

The complaint has effectively frozen his bid for the Westminster seat, with the candidate and his team unable to act or spend money until Lorna Finn, the SNP’s National Secretary, decides what should happen.

Frustrated members of the WCC say that despite the looming general election they have heard nothing from the party in the last six weeks.

“We need the SNP National Secretary to come out with some sort of support for us,” one source said. “That's been lacking. It's been sadly lacking. We need that to happen soon, very soon."

They continued: "It's imploding. It's on the verge of a mass resignation, and it's because of the way Toni's been treated.

"It's my view he's being bullied. I've watched this process since the end of August and he's being bullied and hounded out.

"I never thought I'd speak out like this against the party.

"But there is a cabal. And the people involved in that cabal are Michael Matheson MSP and that's because he came out and endorsed one candidate the night before the vote. That was wrong.

"There's also Cecil Meiklejohn, who's council leader.

"[The cabal] are also in my view, bullying other members of the Western Campaign Committee not to support Toni.

"Every move he makes, they've tried to block. They presented a motion trying to block him from campaigning, which was defeated, but they're now trying to force him out.”

READ MORE: Kate Forbes: SNP must not prolong gender legal battle

Our source said this "cabal" had dominated Falkirk SNP for some time and struggled to accept that their candidate had lost the ballot.

They laid the blame directly at the feet of Mr Matheson. “It's my view that Michael Matheson needs to resign. Not because of the iPad issue necessarily. But because he started all this mess in Falkirk. And he has to go before we can clear it up.”

Asked if they meant resign as Health Secretary or as an MSP, they made clear they just wanted him to quit his role in government.

"I don't think he's fit for purpose anymore,” they said.

However, another senior SNP source in Falkirk said it was “ridiculous” to suggest Mr Giugliano was being bullied.

They told the Herald on Sunday: “I am aware of a number of significant complaints about Toni: that he overspent his budget, then created a fraudulent return, that he misled someone who gave him an endorsement and that he tried to persuade others to withdraw in his favour.

“I think many across Falkirk district are dismayed at his lack of integrity and to claim bullying for behaviour that most people would consider unacceptable is ridiculous.

“The matter is with HQ who also have evidence of each complaint.”

Mr Giugliano said the claims made against him were “simply not true.”

He added: “I’m honoured to have been selected by members in Falkirk and look forward to taking our positive message of hope to voters right across the constituency so they can have an SNP MP who delivers on their priorities.”

An SNP spokesperson said: “We don't comment on internal party matters."

The local woes are the latest headache for Mr Matheson, who is currently being investigated by the Scottish Parliamentary Corporate Body over his £11,000 data roaming bill.

In a statement to MSPs last month, the minister said his teenage sons had watched football during a family holiday to Morrocco, running up the eyewatering charge.

Mr Matheson had initially agreed to pay £3,000 of the bill from his office expenses, with parliament agreeing to pay the rest.

But after learning that his sons were responsible for the bill, he said the family would pay the cost in full.

READ MORE: Yousaf faces clash with Greens amid SNP calls to ditch gender Bill

Mr Matheson’s integrity has come into question over the affair. He claimed he only learned about their use of his parliamentary iPad on Thursday 9 November, following days of media scrutiny over the staggering expenses claim.

However, on Monday 13 November, when asked directly if there was "any personal use" of the device during the family holiday, he told reporters: "No”.

When asked if anyone else could have used the device, he, again, said, "No"