Last week my friend Douglas Ross, leader of the Scottish Tories, made more than waves: he made history. He became the first leader of the Scottish Tory party to call for the resignation of the UK party leader. Even the outspoken Ruth Davidson never did this when she was leader. When the UK party leader is also the Prime Minister of the day, this is quite something.

Douglas acted not out of political calculation but for reasons of principle. Douglas was a minister in Boris Johnson’s government when the Dominic Cummings scandal broke 18 months ago. Douglas was the only minister to resign in protest at what Cummings had done.

Douglas knows that it is not only profoundly unjust, but also deeply unconservative, that the No 10 operation in Downing Street seems to think that the rules which apply to everyone else somehow do not apply to them. That Boris Johnson has allowed this toxic impression to grow and fester is the reason that I agree with Douglas Ross’s judgement: Mr Johnson is no longer fit to lead the party and no longer fit to hold high office.

Douglas will have assumed, when calling for the Prime Minister’s resignation, that the latter’s time was up. He will have assumed that Mr Johnson will not survive the scandals that now engulf what is left of his administration. I thought last week – and I still think now – that this is probably right. I do think that, sooner rather than later, Boris Johnson will be forced out.

The reason is simple – and here the measure is one of raw party calculation. Mr Johnson is not beloved by his political party. For as long as he is an electoral asset – and he is, we must always remember, an election and referendum winner – he will be allowed to remain in place. But the minute that shifts, the minute his roguery is perceived no longer as part of his charm but as a reflection of his monstrously self-serving double standards, and he becomes not an electoral asset but a liability, the party will ditch him in favour of someone altogether cleaner-cut. Rishi Sunak is not the frontrunner by accident.

However, Boris Johnson is also a survivor. He is a ruthless fighter as well as an extraordinary self-promoter. He destroyed not one but two Conservative prime ministers in order to get to No 10. We cannot write him off just yet. All of which poses something of an existential question for the Scottish Tories. What do they and their leader Mr Ross do now if, having very publicly called for the Prime Minister’s resignation, he somehow clings to office and remains in place?

Consider that in March, the Scottish Tories will hold their annual conference. Can Boris Johnson possibly attend it? Consider that in May, we return to the polls in the local government elections. Can Douglas Ross possibly lead a campaign to elect Conservative councillors, when he himself has said that the leader of the Conservative party is not fit for office?

Of course, Douglas might himself resign and walk away. He has done that before. But I earnestly hope he does not. He’s a good man, a man of steel as well as principle, and I admire him greatly. But he needs to find the courage, the discipline and the leadership to do now what Ruth Davidson should have done years ago: break away.

We desperately need in Scottish politics a party of the centre-right that is credible as well as robust. We need that clash of ideas. We need to hear and think about alternatives to the soggy social democracy preferred by both the SNP and Scottish Labour. We on the centre-right have distinctive and important things to say, about the economy and wealth-creation, about how to inject growth and prosperity into the stalling Scottish economy, and about social policy (think, of example, for how Douglas Ross has led from the front on the issue of Scotland’s drugs deaths).

And yet, because of the endless circus of pantomime politics emanating from south of the border, we cannot get these ideas to the table. When Scottish Tories are interviewed, they are not asked about how to build back better, or how to reform Scotland’s struggling schools, they are asked about Boris bloody Johnson.

The argument about a break-away party of the centre-right in Scotland long pre-dates Mr Johnson’s premiership. Those inside the party who are long-time enthusiasts for the idea say “now is not the time”. But now is never the time. There is always a reason of expedience not to make the leap. My question to the party would instead be this: if not now, when? How dire do things have to get before we wake up and realise that, in our current structure, we have more than reached our ceiling? For the truth is that the Scottish Tory brand has peaked and, from here, it will only decline.

That is not because we on the centre-right do not have valuable, relevant and vital things to say about the chronic policy problems modern Scotland faces. It is because we are using the wrong vehicle to drive those ideas forward.

The Scottish Tories have a choice. They could rest awhile where they find themselves, with a quarter of the seats in Holyrood and perhaps a fifth of the popular vote, slapping themselves on their backs that these numbers are a lot healthier than they were a decade ago. Or they could push on from here, and seek something more than being a “stop the SNP” party.

Really good opposition leaders manoeuvre their parties into places in which they can credibly present themselves as alternative governments. That’s what Tony Blair did. That’s what David Cameron did. And that’s Douglas Ross’s opportunity now, if only he wants to take it. Be bold, Douglas, and make a break for it.

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