DAVID Cameron's newly appointed top legal adviser in Scotland has been dubbed politically clueless for predicting an SNP vote for Westminster would be "completely wasted".

Richard Keen QC, who became Advocate General for Scotland two days ago, estimated the SNP would win "half a dozen seats" in the Commons before the election, 50 short of the final total.

He also predicted the Scottish Tories would "improve" their position in Scotland on May 7, only for the party's vote share to slump to its lowest level in 150 years.

Nicknamed the "Rottweiler" because of his tenacity in court, Keen, 61, is one of Scotland's best paid and most respected legal minds.

He had been widely tipped to become Advocate General, and his appointment on Friday means he is now the most senior legal adviser to the UK government on Scots Law.

A former Dean of the Faculty of Advocates, he will become a working peer, enabling him to steer the new Scotland Bill through the House of Lords.

The £128,000-a-year post was previously held by the veteran LibDem Lord Jim Wallace.

Keen had been Scottish Tory chairman for 18 months, but now gives up that role.

Scottish Conservative leader Ruth Davidson said she would miss his "wise counsel".

However, Keen's political skills are not always as sharp as his legal ones.

Asked about the 2015 election prior to the vote, he declared: "An SNP vote for Westminster is a completely wasted vote. What are half a dozen SNP MPs going to do at Westminster? What are they going to achieve? Absolutely nothing."

Keen also foresaw a good night for the Scottish Tories.

"Since 2012 there have been 18 council by-elections and the European elections. In all 19 of those elections the Conservative vote has gone up. I'm not saying massively, but it's gone up. All of that tells you one thing: momentum. With that momentum we will improve, there's no question."

The Tories went on to record their lowest share of the vote in Scotland since 1865.

Reputedly Scotland's best paid lawyer, Keen boasts he is "never knowingly underpaid".

He lives in Edinburgh but also owns an "extremely modest" 16th century castle in Fife. He has a history of controversial remarks.

On his appointment as Tory chair, he said some of the party's MSPs were "coasting" and said a Tory-dominated administration at Holyrood in just 10 years was "realistic".

He also said Alex Salmond was "plainly not a statesman" as First Minister because he did not rise above party politics in government affairs.

Earlier this month, David Cameron ennobled his former special adviser Andrew Dunlop to make him a junior minister to Scottish Secretary David Mundell.

In a previous civil service role, Dunlop helped introduce the Poll Tax under Mrs Thatcher.

An SNP spokesman said: "Not content with appointing the architect of the Poll Tax to a key role in the Scotland Office, David Cameron has now seemingly appointed someone with even an even worse political instinct than his own when it comes to Scotland.

"The fact is that - despite the ludicrous predictions of Mr Keen - this election saw the Tories get their smallest share of the vote in Scotland since 1865.

"People in Scotland continue to reject the Tories precisely because of their outdated attitudes when it comes to key issues like further powers for Scotland."

A Scottish Tory spokesman said: "Almost no-one - including pollsters, journalists and bookmakers - predicted the outcome of the General Election. The SNP certainly didn't, and the impact their MPs will have in Westminster is very much still open to question."