THE SNP have been compared to Ukip, the Front National in France, far right parties in Holland - and even the Tea Party in America - by a senior Liberal Democrat.

A senior source close to party leader and Deputy Prime Minister Nick Clegg said at yesterday's party conference in Liverpool: "You have different kinds of nationalism on the rise in this country. It's by no means unique in this country in times of difficulty; the western world has undergone some pretty pressing difficulties since the crash of 2008.

''You have Le Pen in France, [Geert] Wilders in Holland and the Tea Party in the US. This country is no different... You have Ukip trying to pull us out of one union or the SNP trying to break up the UK. These are forces of nationalism which are wishing to fracture our country; something the Liberal Democrats stand wholeheartedly against."

The comments come ahead of today's speech at conference by Clegg, where he will warn that a vote for the SNP is "not harmless", arguing that if people do not want a lurch to the left with Labour or to the right with the Conservatives, then they should choose the stability of the middle and vote for the Liberal Democrats.

In a question and answer session with delegates yesterday, the party leader insisted the SNP and Ukip were not parties of protest, but parties representing an "ugly form of political grievance".

Danny Alexander, LibDem chief secretary to the Treasury, has already ticked off David Cameron for his "disgraceful" behaviour in "talking up" Nicola Sturgeon's party for what he insisted were the Tories' own political purposes.

The Highland MP claimed that if the SNP ever got to be part of a governing alliance with Labour, they would simply use it to further their aim of Scottish independence and undermine the Union.

In his conference speech, he branded the Nationalists "reckless" and claimed that in their zeal to "achieve what they see as the Holy Grail of separation, they lose all perspective, they take their eye off the ball".

Alexander argued that when it came to the economy, the SNP leadership misjudged "all the big calls", saying that the First Minister's claims that her economic vision would lead to less debt was "factually wrong; her plans would lead to yet more debt not less".

Business Secretary Vince Cable, decried any chance of a Lab-Lib-SNP tie-up after May 7, saying it was "virtually inconceivable that you can have a coalition with a party that is committed to breaking up your country. We just don't see how it could happen."

In his keynote address this lunch-time, Clegg will praise the resilience and steadfastness of what he will term his "brave party", saying it has been tested in government and "has passed the test".

He has said that in the next parliament there will be £1.25 billion of extra funding to "revolutionise children's mental healthcare"; a particular priority for the LibDem leadership. Clegg's spokesman said the details of where the money would come from would be announced in Wednesday's Budget.

A £1.25bn net increase in spending would result in an allocation of around £125 million for the Scottish Government. The spokesman stressed the policy would apply to England only, but that while the issue was devolved to Holyrood, the Lib Dem leadership would "encourage" the Scottish Government to follow suit and prioritise mental healthcare north of the Border.

In his speech, Clegg will also declare that the LibDems "rescued the economy" by going into coalition with the Tories and proved wrong those who said Britain would collapse into chaos governed by a Con-Lib partnership.

He will say: "We challenged the power of the vested interests and we felt their wrath in return - and we are still standing."

Given national opinion polls, one senior source admitted that a "good result" in May's General Election would be losing half of the party's 56 MPs. In Scotland, the LibDems might be fortunate to keep five of their 11 MPs, party sources believe.

The Deputy Prime Minister will tell delegates their resilience under pressure will mean that the party will defy the electoral odds.

He will add: "So when people tell you we can't, tell them where to go. I have a message for all those who are writing us off once again: the Liberal Democrats are here to stay."

SNP MSP Christian Allard said: "We will take no lessons from a party that was on the same side as Ukip and other extreme right-wing elements in the independence referendum.

"As the LibDems teeter on the brink of electoral oblivion, their desperation is palpable. These comments are deeply offensive to the hundreds of thousands of people across Scotland who support the SNP. The SNP stands for a tolerant Scotland playing a progressive role in Europe and the wider world - a far cry from a Westminster establishment which is dancing to Ukip's intolerant tune."

SNP Deputy Leader MP Stewart Hosie said: "This is desperate stuff ... After five years in government propping up the toxic Tories, all Nick Clegg and his party have to show is a trail of broken promises ...Unlike the LibDems, we have made clear we would never prop up a Tory government. It's no wonder Scotland sees the SNP as the party to make sure the things that matter to them are firmly on the Westminster agenda. Only a strong team of SNP MPs will work to build a progressive alliance at Westminster."