A SENIOR Tory MSP has urged voters to “back anyone but the SNP” and support other Unionist parties, including Ukip and Labour, to derail a second independence referendum.

Murdo Fraser, Ruth Davidson's finance spokesman at Holyrood, has called on voters in the council elections on May 4, after voting Tory, to cast their next preferences votes for other parties – to cause maximum damage to the SNP.

Scotland's local council elections operate a preferential voting system, in which electors rank the candidates in order of numerical preference.

While Fraser does not explicitly state which parties he believes voters should support, those that favour the Union are Ukip, Labour, the Lib Dems.

By not giving any preferences to the SNP it would mean the party suffered more losses and would be a setback to Nicola Sturgeon's plans to hold a second referendum, Fraser said.

Fraser, widely viewed as being on the right of the Tory party, made the call in a signed letter to voters, obtained by the Sunday Herald.

He says the approach is needed to prevent Sturgeon's "irresponsible threat of a second independence referendum".

His intervention represents a departure for a senior mainstream Unionist politician in urging support for other anti-independence parties in order to halt the prospect of a fresh referendum. In effect he is calling for an electoral referendum on a referendum.

Fraser, the MSP for Mid Scotland and Fife region, also talked about the need to “send a message to Nicola Sturgeon" in his letter to his voters.

He said: "Whilst local issues are always important, overshadowing this election is Nicola Sturgeon's irresponsible threat of a second independence referendum. This is your chance to send her a message.

"Every advance for the SNP at these local elections will be taken as an endorsement of a second referendum."

In an uncompromising rallying cry to Unionists to use the preferential voting system to maximise SNP losses and set back the prospects of an independence referendum he said: "Remember this is a preference voting system with no wasted or tactical votes.

"To stop the SNP use your first vote 1 to back the Scottish Conservatives and subsequent votes (2,3 etc) to back anyone but the SNP."

Fraser also said: "Don't give Nicola Sturgeon's plans a boost by voting the SNP back into power in Fife" – again emphasising that the council elections are a chance to deliver a verdict on the First Minister's plans for a second referendum.

His letter also includes a bar chart next to a headline stating "how to stop the SNP here" which sets out the level of support polled by the main parties in the Mid Scotland and Fife region at the 2016 Holyrood election.

It shows the SNP on 41.3 per cent of the vote, compared to 25.2 per cent for the Tories, 17.6 per cent for Labour, 7 per cent for the Lib Dems and 6.1 per cent for the Greens.

It is intended to make clear to Unionist voters that if they express second and third preferences for anti-independence parties after the Tories there will be a better chance of defeating the SNP.

The letterhead of the letter is 'Murdo Fraser MSP - Scottish Conservative and Unionist MSP for Mid Scotland and Fife'. At the bottom it has the logo 'Fife Conservatives'.

Last night, the SNP said a willingness to potentially advocate support for UKIP candidates showed the desperation of the Tory local election campaign.

SNP MSP Shirley-Anne Somerville said the Tories are "fast becoming Scotland’s UKIP" and talked about "how far the Tories have lurched to the right".

She said: “The Tories have become born-again Brexiteers since the EU referendum, but the fact that they’re now endorsing UKIP will shock even their most loyal voters."

A Scottish Conservative spokesperson, in response, said: “Only a vote for the Scottish Conservatives will elect councillors who will provide a strong local voice and send a strong message to the SNP - No to another divisive referendum, Yes to strengthening our communities."