Boris Johnson has appointed the Scottish Tories’ director as a new special adviser in an attempt to get his Union strategy back on track.

The Prime Minister is to make Lord McInnes of Kilwinning his special adviser on how to bolster the Union and fight Nicola Sturgeon’s plan for another independence referendum by the end of 2023.

Senior Scottish Tories expressed delight at the appointment, with Ruth Davidson, the former Scottish Conservative leader, saying it was "thoroughly positive all round" and that the UK Government was "finally getting it."

Mark McInnes has been director of the Scottish Tories for 18 years and was a director of the victorious pro-UK Better Together campaign in the 2014 independence referendum.

He also played a pivotal role in masterminding the Conservative revival in Scotland, with the party picking up a record number of votes in the recent Holyrood election and stopping Ms Sturgeon’s SNP from winning a majority.

Mr Johnson originally created a "Union unit" in Downing Street to advise him, but it was scrapped earlier this year following the departures of its two heads, Luke Graham, a former Scottish MP, and Oliver Lewis, a Vote Leave veteran, in quick succession.

Ms Davidson said Lord McInnes’s appointment signalled a return to a "more traditional advisory network" as Mr Johnson attempted to revamp his anti-independence strategy.

A senior insider told The Telegraph: "There will be a proper adult in the room the Prime Minister listens to. Downing Street gets the success that he has had in Scotland, and he goes into that role with more credibility than anyone else has since Boris Johnson became Prime Minister."

They said Mr Johnson did not know Mr Graham, the former Ochil and South Perthshire MP, and "we need someone who will say that is or is not going to work for Scotland and here’s how the Nats will react".

As well as advising Mr Johnson on strategy, Lord McInnes is an expert on conducting polling and focus groups to ascertain Scots’ views on key issues.

His strategy in the Holyrood election of focusing on stopping a second independence referendum received criticism but provided effective after focus groups showed many voters wanted a party that was strong on the Union.

Announcing his new role, Lord McInnes said: "I want to say a sincere thank you to all the party members, activists and supporters who it has been my pleasure to work with over the years.

“Together we have achieved so much, helping win the 2014 referendum, contributing to the election of Conservative governments, and firmly establishing the Scottish Conservatives as Scotland’s second-biggest party and real alternative to the SNP. I know that the party will go on to even greater success in future."

Mr Ross said Lord McInnes "has been central to the renewal of our party over the last decade and has made an invaluable contribution to the Conservative and Unionist cause".

His successor as Scottish Tory director will be appointed in due course.