NICK Clegg has called on Tory and Labour supporters to vote tactically in an effort to stop Alex Salmond returning to Westminster as the Liberal Democrats suffered a fresh opinion poll setback in Scotland.

The Lib Dem leader visited Gordon, where the former first minister is hoping to win on May 7 to warn that Mr Salmond wanted to "pocket" votes in order to "strut his stuff" in Westminster.

Mr Clegg said only his party is capable of preventing the former SNP leader returning to the Commons where he could potentially keep a "hapless" minority Labour administration on "life support" in a vote-by-vote deal.

He urged voters across Scotland to put aside traditional party allegiances to support his colleagues in seats where the Lib Dems are facing an SNP challenge.

But in a further sign that the SNP surge could cost the Lib Dems dear in Scotland, constituency polling by former Tory peer Lord Ashcroft indicated the party was far behind in four of its 11 seats.

Among those running for re-election, coalition minister Jo Swinson and former leader Charles Kennedy are 11 and 15 points behind respectively in East Dunbartonshire and Ross, Skye and Lochaber.

The SNP look like winning North East Fife, which has been held by the retiring Sir Menzies Campbell since 1986, with the poll indicating a 13-point SNP lead.

In Berwickshire, Roxburgh and Selkirk, former Scottish secretary Michael Moore is behind in a three-way race.

The Tories hold a one point lead in the constituency.

A Lib Dem source dismissed the polls as "irrelevant" because they did not name the candidates, insisting that the party's MPs had strong personal support.

Mr Clegg used a visit to a livestock market in Inverurie to call for Gordon voters to put aside their traditional allegiances to halt Mr Salmond's progress to Westminster.

He said the former SNP leader "appears to believe that the Gordon constituency is a pit stop on his international book tour".

On a campaign visit to support Christine Jardine's effort to hold the seat for the Lib Dems, he appealed "to all those voters, they may be Labour voters, they may be Conservative voters, but voters who simply don't want to have their vote taken for granted by Alex Salmond".

He added: "If you want to stop Alex Salmond pocketing your vote and dancing off to strut his stuff on the Westminster stage, the only way to stop him is to vote for Christine Jardine as the next MP for Gordon."

Former MP Sir Malcolm Bruce had held Gordon for the Lib Dems since 1983, but the scale of the challenge facing Mr Clegg's party was illustrated by a Lord Ashcroft poll in January which put the SNP on 43% with the Lib Dems on 26%.

Mr Clegg warned that the SNP wanted to reopen "old wounds" from the divisive independence referendum campaign that had strained families, friendships and communities.

The Lib Dem leader said: "The people of Scotland don't want to turn the clock back and reopen those wounds about that debate, they want to move forward."

Mr Clegg told reporters that the SNP offered the "politics of division" while voters "want the politics of hope, of unity, of continuity".

He dismissed as "ludicrous" suggestions that it was hypocritical to urge supporters of other parties to back the Lib Dems to stop the SNP if he was not prepared to tell his voters to put their cross in Labour's box in seats where Ed Miliband's party is battling the nationalists.

Speaking to reporters on his campaign bus, he said: "It's not for me to start telling Lib Dem voters to do anything other than vote Lib Dem. What a ludicrous idea."

Mr Clegg said it was "theoretically possible" that the Lib Dems could come out of the election with more seats than Labour in Scotland because of the damage the SNP surge could inflict on Mr Miliband's party.

He said: "I try to avoid making predictions, but I'm quite seduced by that prospect."

Mr Clegg blamed Labour's failings for the current political landscape in Scotland.

"We'll see where it ends up but I suspect we'll weather the challenge from the SNP a lot better than Labour does."

The SNP dismissed Mr Clegg's call for tactical voting.

MSP Christian Allard said: "Calamity Clegg has blundered yet again. He is calling on people to vote tactically in Scotland, yet tactical voting campaigners are actually urging people to vote Tory in four of the Lib Dems' own seats - over a third of their total - and in one Labour-held seat.

"It is abundantly clear that the tactical voting campaign is a Tory front - aiming to elect more Tory MPs in Scotland, which would make David Cameron walking back into Downing Street more likely."