All political careers end in failure and, if the lessons of history are anything to go by, some of the biggest failures are those who go at a time of their own choosing.

Alex Salmond and David Cameron stepped down because they had finally run out of road, having lost career defining referenda.

Tony Blair and Harold Wilson both left office mid-term, apparently on a high, but behind the scenes there were irresistible pressures for them to quit. In the case of the former, there was the brooding presence of Gordon Brown, demanding payback for a pact agreed privately 13 years previously while the latter, we learned later, was in the early stages of dementia.

Nicola Sturgeon’s shock resignation as Scottish First Minister two years ago was accompanied by a load of waffle about having nothing left in the tank, signally failing to mention the small matter of a police investigation into SNP finances that would later result in she and her husband, Peter Murrell, being arrested.

She was subsequently released without charge and denies any wrongdoing, while Mr Murrell – the party’s former chief executive – is awaiting trial after having been charged with embezzlement.

Read more by Carlos Alba

Her announcement last week that she will not seek re-election as an MSP in next year’s election brings the curtain down on the career of one half of a double act that has defined the SNP for a generation.

Following the death of her predecessor and mentor Mr Salmond last year, the party and the wider nationalist movement are now at a tipping point, and the direction taken by the former will determine the fate of the latter – and perhaps the country – for the next generation, perhaps forever.

There are signs that next year’s Scottish Parliament election will mark a significant........

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