The controversial politician Enoch Powell once said that all political careers, unless cut off in mid-stream, end in failure.

As Nicola Sturgeon starts her departure from the leadership stage after standing down as SNP leader and First Minister, it may be hard to watch the final days of her time at the top and argue otherwise.

In a very personal statement the First Minister laid out her achievements in an unexpected announcement – but she also underlined the thing that she’s spent most of her adult life doing – working for her party to get independence for Scotland.

While in one sense, as the dominant force in Scottish politics, her party will never be closer to achieving that aim, the conundrum is that goal is equally as far away as ever. The truth is, there is no vote on the horizon and polling suggests many Scots remain unconvinced.

Delivering it, if it is ever delivered, will be done by someone else (though I’ll come back to that scenario later). That could be Kate Forbes, Angus Robertson or someone we’ve yet to hear of but it also might be no one.

Is independence dead?

Independence, or more precisely the credibility of creating an independent Scotland, has been at the core of the SNP’s meteoric rise to power and provided a helpful antidote for the SNP to the virus of policy failures that has impacted its time in government.

Since 1990, apart from a brief interlude when John Swinney had a go, only two people have held the leadership banner aloft – Alex Salmond and Nicola Sturgeon. Salmond departed after the failure to win the 2014 referendum; Sturgeon never even got that far. Putting that into context, that’s as many leaders as the Tories have had since July last year.

But ultimately, despite the considerable force of those individuals, they have failed. Scotland is still part of the UK. Support for separation has grown but is firmly stuck in the mid-50s at best and mid-40s at worst. As she herself acknowledged, the message may be better delivered by someone about whom the electorate doesn’t already have a fixed view.

The First Minister leaves with the highest approval rating of any UK leader and eight election wins including two emphatic victories in Scottish elections. The nearest opposition challenger is miles away – both in support and in personal rating – but there is a lingering suspicion that Sturgeon’s approval ratings were on a downward trajectory and taking with it support for separation.

By acting now, the First Minister and her party will hope to re-invigorate the cause as we enter the run up to the next UK General Election.

Nicola Sturgeon was a woman of firsts

It’s worth taking a moment to consider her legacy. Sturgeon the second First Minister from the SNP but the first female leader of the Scottish Government. Female leaders in the UK remain rare; female leaders from a working class background even rarer. Many of her senior ministers and advisers are female and the make-up of the SNP benches in Holyrood shows that she has blazed a path for others to follow.

Her record on policy though is mixed at best and the Scottish economy remains behind the rest of the UK.

Holyrood is limited in what it can do on many issues and she has focused on supporting vulnerable parts of society. In areas such as economic development, there is little to boast about and the ongoing fiasco around the delay to ferries being built on the Clyde will linger long in the memory.

Her commitment to delivering a green economy has led to challenges in heartland SNP areas such as the North-East where some argue for a better transition from fossil fuels.

An alliance with the Scottish Greens has delivered two ministerial posts and a heavy influence on policy that has also led to mixed results. Will the alliance survive her successor’s election?

Sturgeon has also been the architect of the SNP’s current plan to get a new Indy Ref vote, leading to splits within the party and no doubt has played a part in ousting her supporter Ian Blackford from his role as Westminster leader.

Blackford’s replacement Stephen Flynn is less of an acolyte and may now be buoyed by her departure.

Is this really the end of an era?

A new leader will have a new mandate but how different will that be?

It could be very different.

Sturgeon’s was pretty similar to Salmond’s which means things haven’t changed that much since he first became leader in 1990 – which is the year that Kate Forbes, the most likely successor to Sturgeon, was born.

And finally is this really the end of an era? As Sturgeon steps down consider when Salmond did the same in 2000 and John Swinney took over. Swinney’s time wasn’t great for the SNP and in 2004, despite saying he wouldn’t, Salmond came back as leader with Sturgeon as deputy. In 2007 he won power at Holyrood for the first time.

The next General Election is at least 18 months away. If the new leader fails to deliver, could the party faithful persuade a rejuvenated Sturgeon to take the reins once more and motivated by her failure to achieve her main goal, might she come back for another try?

John Penman, Partner