LABOUR are probing their former candidate in Shetland after he encouraged voters to back the SNP in yesterday’s by-election.

In a letter to the Shetland News, Peter Hamilton said voting for Nicola Sturgeon’s man on the islands would help stop Boris Johnson and Brexit.

It is against the party’s rules for members to publicly encourage support for another party.

Alastair Campbell, the former communications chief to Tony Blair, was expelled from Labour in May for saying he voted for the LibDems in the European elections.

In his letter to the local paper, Hamilton said: “We are where we are right now, and I risk my Labour Party membership (which I hold dear and support by standing order each month) by writing this, but we have to address the greatest threat.

“As a life-long Labour Party member and former Scottish Labour candidate for the Scottish Parliament (with strong Green sympathies ), who has been impressed by our candidate’s campaign, I am obliged to make this urgent appeal to all readers: seize the day and deliver the result the UK, Scotland and Shetland needs – Vote SNP, stop Boris.”

He added: “I expect at this point Ruth Davidson would also agree.”

Scottish Labour told The National: “We’re aware of this and will look into it.”

Hamilton was the party’s candidate in the 2003 Holyrood election. He finished in fourth place, winning just 880 votes.

Labour’s rulebook says that any party member who supports a political organisation other than Labour, or supports any candidate who stands against an official Labour candidate, is ineligible to be or remain a party member and is therefore automatically excluded from membership.

When Campbell was expelled, shadow minister Dawn Butler said that any member who said they had voted for another party would automatically be excluded. “It’s just part of the rulebook,” she told the BBC. “Everyone knows that.”

By the time you read this, the result of the by-election should be known.

The vote was sparked after Tavish Scott, who has represented the area since the Scottish Parliament was established in 1999, stepped down.

He is leaving Holyrood to take up a position with Scottish Rugby.

At the time he said it had been an “enormous privilege and honour” to have served the area as an MSP.

The SNP has been campaigning hard in the constituency, with First Minister Nicola Sturgeon making three visits in support of her party’s candidate Tom Wills.