If John Swinney never did another thing for independence, the SNP and for Scotland, he would still have done more than any other figure in the party's history. We all owe him big style. 

He has given much of his life to it, and the positive effect of that contribuiton over the years is clear. We should all wish him, Liz and Mathew the happiest of times together as he leaves the post of Deputy First Minister at the end of March. He will continue to be the MSP for Perthshire North and, I am sure, a formidable voice in the counsels of the SNP for a long time to come. 

He will be 60 next year, but remarkably he has been a senior member of the party's leadership for more than 35 years, taking over in the key role of national secretary when he was only 22. He held various internal elected positions before becoming deputy leader on the death of Alan Macartney in 1998, and was resoundingly elected leader two years later with two-thirds of the votes, having been challenged for the post by Alex Neil. 

READ MORE: John Swinney to quit government after nearly 16 years

As leader he introduced the one member, one vote democratic system which was being opposed by some vested interests. They even mounted a challenge to him at the SNP conference in 2003 but he remained steadfast. His courage in securing the firm foundation of member participation bore fruit in the succesful elections to the Parliament from 2007 onwards. 

John won the Westminster seat of Tayside North in 1997 and held the slightly altered constituency in the first Scottish Parliament elections two years later. When the SNP came into government in 2007 he not only led the negotiations with the civil service behind the scenes but was the obvious choice to fill the key, sensitive and very demanding, finance portfoio which he did for a record-breaking nine years.

That combination of discreet behind-the-scenes activity with front-of-house leadership is very John Swinney. You can trust him to keep confidences and to give quiet discreet advice. You can also rely on him to secure what he believes is right privately, publicly and politically. In happier days when the Scottish Parliament was less nakedly and cruelly partisan, that was recognised across the chamber and by those outside the Parliament too. His handling of the relationship with Scottish local government was particularly crucial and was a key factor in our success as a minority government from 2007 to 2011. 

Sometimes the strength and determination of his views surprised even those who knew him well. I recall how startled I once was to see him bang the table at a fractious meeting before which he had firmly instructed me to keep cool. As ever, though, his instinct was right.

He was education secretary for five years and having held the same job for the same length of time I know how much it must have taken out of him, though also how fulfulling it is. Latterly he has combined the post of deputy first minister - competently providing the calm centre in very tricky times - with that of leading the process of Covid recovery, whilst also covering the finance portfolio during Kate Forbes's maternity leave.

It is impossible for any human being to take on that unique mix of heavy burdens without feeling them and his friends knew that at some stage it would have to end. 

Nonetheless, his decision first of all not to contest the leadership when Nicola Sturgeon unexpectedly resigned and now his announcement that he would step away from Government when she left marks a huge break with the past for the party and the Government, whilst creating a number of vacancies (not just one, he did so much) that will be hard to fill.

The National:

John and Nicola are the last governmental members of a small group that, as Philip Sim of the BBC observed some weeks ago, steered the party over 30 years or so from the fringes of Scottish politics to its present dominant position at the centre. That group is now stepping into the sunset. A new generation is coming forward to lead. 

Nonetheless I am sure John will be there to give advice when asked, as my own experience proves. 

Although we have had our differences, I remember with gratitude those early days when, as a young, and unexpectedly elected vice convener of the SNP John as national secretary helped me to find my feet. We both quickly came to know the value of loyalty in politics, and the need for trust even if there are disagreements and differences in outlook and character. 

He is a man with a deep religious faith and with far less doubt than I have. I shall therefore continue to advise those starting out in their ascent of the greasy pole of politics, as Disraeli called it, to learn from the honest, talented, kind, generous and often witty John Swinney. And I will certainly go on doing so.