Liberal Democrat leadership candidate Tim Farron has launched a ferocious attack on the SNP accusing the party of becoming the very thing it despises with its authoritarian,'Big-Brother' style approach to power.

Mr Farron described the party's attitude to civil liberties as "terrifying".

"They are doing the worst and darkest things that people suspect nationalists to be in favour of anywhere in the world," he said.

"My take on the SNP is that they are avowedly centre-left and extremely authoritarian."

In an interview with The Herald, Mr Farron accused the party of politicising the police and hit out at a controversial move by Edinburgh 's SNP-Labour council to beef up city-wide CCTV surveillance.

He also ruled out any job for Lord Rennard, the peer who faced accusations of sexual harassment from female LibDem candidates.

Mr Farron said he thought a third 'devo max' option should included in any future independence referendum.

The SNP last night accused the LibDem MP of attention seeking.

Mr Farron is seen by some as the favourite to succeed Nick Clegg, who resigned in the wake of the LibDems disastrous General Election result.

After five years in coalition with the Conservatives the party slumped to just eight MPs.

Mr Farron has faced questions over his Christian faith and his decision to abstain on a vote on gay marriage - which he has since said he regrets.

As party president he also never took a government job in the coalition, unlike his opponent, the respected former minister Norman Lamb.

Mr Farron said if he won his party would vigorously challenge the SNP on civil liberties.

He branded the party's approach to power "terrifying to anyone who treasures traditional Scottish values and traditional Scottish liberties. "

He said: "I think the SNP have to understand that they have become a beast they would rather not be.

"In the words of James Grant from (the band) Love and Money... 'As you reach for the stars in your eyes, You become the very thing you despise'."

He added: "There is a sense which nationalism which talks about a sense of liberation from the yoke of Westminster and freedom and progress actually ends up becoming a beast, nastier even than the one they were trying to slay.

"That is the danger. Nationalism can be a force for progress when it is insurgent. It is almost without exception a reactionary force when it is ascendant, and I don't have to go into too much detail for the evidence for that," he said.

He added: "Nobody who voted SNP wants to think they are an arrogant, authoritarian illiberal Big Brother entity. It is not something that right-thinking Scottish or British people of any kind would want to have thought of them. But that is who they are and only Liberals will challenge them".

He added that the SNP had "centralised and politicised the police in a way that makes Theresa May look like a Liberal".

SNP plans for a "super ID" national database made Tony Blair look a Liberal in comparison, he added.

On devo-max, he said: "it should have been on the ballot paper" last September.

Asked if he would want a devo-max option included in any future referendum, he said: "Yes, I guess that would make sense.

"The Scottish party would make that choice and I would respect that choice. But I am sure they would consider that".

On Lord Rennard , Mr Farron blamed a "lack of professionalism and a naivety in dealing" with the allegations.

That, he said, "let everyone down, that includes Chris Rennard and that includes certainly the women".

But, he added: "I would not be appointing him to any position of any kind whatsoever should I be leader."

He said he believed in forgiveness, "But I also believe that the women involved are the people who - it is not for me to forgive, it is for them to forgive. It's not been done to me. "

A party inquiry by an independent barrister concluded last year that while the women's claims were "broadly credible" they could not be proved beyond reasonable doubt.

The new LibDem leader will be announced later this month.

An SNP spokesman said: "Tim Farron sounds like a small boy saying rude words to attract attention from grown ups.

"His remarks are ridiculous and embarrassing to his own party - they are so wrong that they underline why his party was comprehensively rejected by the people of Scotland last month, and in the 2011 Holyrood election."