JUST before she sealed a comfortable victory over Ed Davey in the ‘other’ party leadership contest recently, Jo Swinson said that she would love to be Prime Minister. On a scale of one to ten, just how ridiculous a statement is that, where one is 'not at all', and ten is 'absolutely off the charts space cadettery'?

Well, it’s not a one. But it’s not a ten either. Massive, once-a-century change is easier to say than to do, but it seems clear that we do sit at the nexus of what may be the biggest political realignment of our lives. On the face of it, the Liberal Democrats are in a prime position to exploit that realignment and become its biggest beneficiary.

The fact that people are even talking about it is something of a miracle for a party which was thought of as being clinically dead. The leadership of Vince Cable, notwithstanding the fact he is a perfectly able man with a good record in government and opposition, was, to test the boundaries of the meaning of the word, ‘quiet’.

However, an event – Brexit – has brought the party back to life, and the election of the energetic Jo Swinson has pumped more adrenaline into it. There are parallels here to the Scottish Tory party, which was finished until the event of the Scottish independence referendum gave it a reason to exist. The Lib Dems have become the party of Remain; the Scottish Tories did the same with Unionism. The Lib Dems are now led by a young woman who looks and sounds and feels like a normal person; the Scottish Tories benefit hugely from another one, Ruth Davidson.

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But here’s where Jo Swinson needs to learn the lessons and consider what can go wrong. There is a reason why the Scottish Tories talk about a second independence referendum as much as, or more than, the SNP. They need it. It is the foundation for their single-issue campaign, which has already stretched across three Scottish and UK general elections, to great success, and is about to encompass another, in 2021. Without the second independence referendum, and the ability to whip the unionist vote into a frenzy, what do the Scottish Tories have? Not much, in truth. A set of good, competent people, who would be perfectly able to run a government, but no policy platform to make wavering voters – the ‘maybes’ – feel compelled to tick the box with the C-word in it.

Herein lies the lesson for Jo Swinson. The Liberal Democrats, today, is a single issue party. It is a party of Remain, setting itself apart from two parties of Leave (the Tories and the Brexit Party) and Labour, a party with a pro-Leave leader who occasionally nods to a change of direction to keep the inhabitants of the tent inside.

But, hard as it is to believe today, the Brexit issue is going to go away, and when it does there needs to be something to fall back on. This is precisely the trap that The Independent Group, or Change UK, fell into, and if the Scottish Tory analogy is too far from home for Ms Swinson to contemplate, perhaps this one is easier.

Change UK formed with the twin aim of becoming an enduring party of government and stopping Brexit, but reality slapped them in the face with swift, ruthless aggression. You can’t be both. You can’t be a narrow single-issue party which welcomes only pro-second referendum Remainers and simultaneously be wide enough to be an enduring party of government.

So, perverse as this may sound for a party with a hand on the shoulder of 48 per cent of the population, the success of Jo Swinson and the Lib Dems is not about Brexit. Brexit is, instead, a bridge for the Lib Dems to the real promised land.

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That promised land is an extraordinary gap in the political party market in the UK. In Europe it would be called social democracy; in Britain, we might better know it as Blairism.

As a party of the centre-right, the Tories will never occupy that space, even if Boris Johnson reclaims his ‘One Nation’ history. Conversely, Jeremy Corbyn’s Labour party has utterly vacated this centre-left, social-democratic ground and shows no desire whatsoever to return to it.

This is Jo Swinson’s ground. She is Emmanuel Macron. She is Stefan Lofven. She is Mette Frederiksen. Except they’re all in office, and she’s not.

In practice, this means a gradual but holistic policy shift, and a shift in attitude away from being a party of protest and towards being a realistic party of government. The party’s social liberalism is in the right place, but it is combined with a message on the economy and on public service reform which is left-wing, interventionist, and bears all the hallmarks of a party of protest which has quickly forgotten the realities of government.

If Ms Swinson wants to be Prime Minister, these are the strategic changes which will have to be addressed, and the tough choices which will have to be made.

In Scotland, there will be a fascinated observer. Willie Rennie, Ms Swinson’s Scottish counterpart, is further from power, but also has an opportunity to exploit a gap in the market. Arguably, his position is even more unique. Only one party in Scotland combines a belief in remaining in the EU, in common with 62 per cent of the population, and remaining in the UK, in common with 55 per cent of the population –Mr Rennie’s.

In common with Ms Swinson, to achieve this needs not just the right message, but numbers. With a paltry five MSPs, Mr Rennie can fill a taxi, but not a Cabinet. Just as, if I were Ms Swinson, I’d be looking for another 100 Chukka Umunnas to defect, if I were Mr Rennie I’d be looking to start with 5-10 disaffected social democrats from the Scottish Labour MSPs at Holyrood.

They exist, and they have far more in common with the Lib Dems than they have with the 2019 incarnation of the Labour party.

This needs one thing which is hard to come across. Courage. Politics is a tribal business, and leaving the tribe is hard. Few make the jump. If we want a better country, and better politics, we need a straw to break the camel’s back.