MIKE Russell, Nicola Sturgeon's key cabinet minister on Brexit, is to stand down at next year’s Holyrood election.

The 66-year-old said someone younger was needed to cover his sprawling Argyll & Bute constituency.

Mr Russell has been at the heart of Ms Sturgeon’s government since the EU referendum of 2016, leading negotiations with the UK Government on Brexit.

He also steered the recent Referendums Act through Holyrood paving the way for a second independence referendum, should the UK Government agree to it.

A former SNP chief executive, he is close to Alex Salmond.

Mr Russell is the fifth - and most senior - SNP MSP to confirm they will leave parliament next spring.

Backbenchers Richard Lyle and Gail Ross and committee conveners Bruce Crawford and James Dornan have also announced exit plans in recent days.

The wave of announcements comes as SNP branches choose their candidates for 2021, and other retirements are expected.

Mr Russell, who was a South of Scotland list MSP for eight years before being elected in Argyll & Bute in 2011, had a majority of 5,978 over the Liberal Democrats in 2016.

He told his constituency association in Tarbert today of his decision, saying he intended to continue his role in government and promote independence and EU membership.

He said: “I have been the MSP for Argyll and Bute since 2011 and it has been an enormous privilege as well as a greatly enjoyable task.

“However I will be 67 this summer and 72 at the end of the next Parliament. Argyll & Bute is a massive area to cover – with 23 inhabited islands and a large swathe of the mainland – and I am getting to the stage of thinking that someone younger would be better able to fulfil all the demands of the constituency.

“It is, I think, much better I say that now than wait for someone else to do so.

“I am proud of the work the SNP in Government has done in Argyll & Bute, securing much new investment, supporting individuals and communities.

"I am also proud of the work that we as a party have done in Government, including the tasks that I have undertaken in my ministerial roles in education, culture, the environment and in improving electoral law.

“Of course, my biggest challenges have been those I have faced since August 2016 when I was tasked by the First Minister with attempting to secure Scotland’s place in Europe and to make Scotland’s voice heard in Whitehall.

“There is no doubt that we are now faced with the most hostile, arrogant, heedless and thoughtless UK Government in many generations, which is determined to have its own way no matter what the people of Scotland want or vote for.

"It has been particularly distressing to have to see Scotland dragged out of Europe against our will by them – though that is something I am sure we can reverse before too long.

“Over the next year I will continue to work on that aim, to develop a greater domestic and international understanding of the case for independence.”

Mr Russell, who was born in Bromley in Kent, said he still intended to stay active in "the political sphere" after leaving Holyrood.

He said: "I think of my decision as stepping back from some current roles, not stepping away from my commitment to our country and the better future it can have and should choose.

“Independence is so much closer than it was when I first voted for the SNP 46 years ago. I hope I have contributed something to that success and I still hope to contribute more but in a different way and role."

Also leaving at the election are Tory MSPs Ruth Davidson, Peter Chapman and Margaret Mitchell and Labour's Neil Findlay.