WESTMINSTER is back today from its long, English public school holidays. We will have a brief parliamentary fortnight of business then another break for the annual conferences of the main Unionist parties. The regular October SNP conference always falls outside this cosy schedule, but then Scotland is always an afterthought as far as Westminster is concerned.

The end of summer recess means that Theresa May’s government will no longer be able to dodge making hard choices about Brexit. Not that the Prime Minister is all that keen to come off the fence on anything, thereby exposing the den of hissing serpents that make up her fractured party. Thus her appearance on the Andrew Marr Show yesterday was a case of the bland interviewing the bland. Mr Marr lobbed gentle underarm questions and Mrs May batted them into midfield without breaking sweat. Anyone watching was none the wiser – which was, I presume, the whole intention.

Mrs May wants to be seen as a reincarnation of the Blessed Margaret. Bulletin from the front line: she is definitely not Thatcher Mk II. You could see that immediately in the Marr interview when May pointed refused to answer any of Marr’s easy questions: on what deal she was seeking with the EU, on bringing back grammar schools or on accepting Scotland’s right (if it so wished) to hold a second independence referendum. Instead we had well-practiced evasion and dissembling. The Iron Lady, in similar circumstances, would have pummelled Andrew Marr – once a stalwart of my old Portobello Labour Party branch – into the studio floor with a clear ideological defence of her positions on everything under the sun.

I’m not suggesting for one moment that Theresa May lacks political steel. Her appointment of the Three Brexiteers – Boris Johnson, David Davis and Liam Fox – to competing ministries is a classic “divide and rule” manoeuvre that leaves Mrs May secure in Number Ten for the moment. Already the summer has been given over to turf wars across Whitehall. The new “super” Department for Business, Energy and Industrial Strategy is rumoured to be riven by in-fighting between its constituent staff from the former energy and business ministries, with the energy people swamping the latter. Meanwhile, David Davis has been in Ireland to explain that regardless of the Brexit deal, there will be no border controls between the Republic and the North. I assume the same goes for an independent Scotland, David?

Sooner or later, the Prime Minister will have to make difficult choices regarding EU strategy. For instance, whether to stay inside the Single Market, or not.

The City of London has recovered its nerve after the unexpected vote to quit the EU and is throwing money at a PR offensive to persuade the May government to negotiate a deal for the UK to remain in the Single Market. That way the banks keep their access to Europe.

But such a deal would mean the UK having to accept EU law – anathema to the Tory populist right. It would also play into the hands of Nigel Farage, who is on the verge of setting up yet another Nigel Farage Party.

London media opinion has it that the Tories are in a strong position because of the existential split in Labour. But the unexpected pro-Brexit vote that dished David Cameron and George Osborne suggests otherwise. The Tory vote has been in decline in England as well as Scotland, over the past two generations. There is every possibility that a properly led and financed movement of the populist right in England could drain support from both Conservatives and Labour. Already, Aaron Banks, the millionaire businessman who bankrolled Ukip's Leave.EU campaign, has said he wants to start a new political party. I questioned Banks in the Treasury Select Committee and he is a cool, calculating customer. Watch this space.

Meanwhile, across the aisle, what is afoot in the so-called official opposition party? Recent polling evidence suggests that Jeremy Corbyn is on his way to a second leadership victory despite the opposition of most of his Westminster MPs. What happens then? There is the possibility that the bulk of Labour MPs could simply operate as a faction independent of the Corbynistas – without actually splitting from the party. They might, for instance, simply reinstitute elections for the Shadow Cabinet, which they would win. They might then offer to work with Jeremy as the elected party leader – a poison chalice if ever there was.

Alternatively, a victorious Corbyn might offer some accommodation to his critics in the parliamentary Labour party. Cutting a deal on shadow portfolios might tempt back at least some of the doubters. However, it’s difficult to see the majority of Labour MPs being comfortable with a compromise, given all that has passed. Any deal would be unstable and likely to blow up as both factions slug it out in the coming reselection contests at constituency level.

Even if Corbyn is ousted by the parliamentary party, Labour remains in deep trouble. For starters, has anyone noticed that Owen Smith – the man who appeared from nowhere to lead the fight against the Corbynistas – has committed Labour to a programme far to the left of where the party was even under Neil Kinnock? This shift to the left has been forced on Smith in order to counter the anti-austerity rhetoric of the Corbynistas.

So Smith has come out for a 15 per cent tax on unearned wealth, re-nationalisation of the railways and even making the Labour conference the sovereign policy-making body again. Does anyone believe the old Blairites now backing Smith believe a word of this? A Smith victory would see these promises binned within weeks.

All of which suggests that a deal between Corbyn and the Labour right-wing can be – at best – only a temporary truce. Which leaves Speaker Bercow with a big constitutional headache: who to recognise as the official opposition. This matters because the Leader of the Opposition gets a public salary of £74,000 plus important rights to question the Prime Minister in the House and nominate subjects for Westminster debates. In normal circumstances, identifying the de facto Leader of the Opposition is easy – which is why the official handbook of parliamentary procedure, Erskine May, has little to guide on the matter. But if Labour at Westminster splits into warring factions, we could have a mini constitutional crisis, with Speaker Bercow as referee.

Of course, there is one united, coherent and effective opposition voice at Westminster: the SNP. However, optimist that I am, I doubt if Mr Speaker will nominate the Right Honourable Angus Robertson MP as Leader of Her Majesty’s Most Loyal Opposition. Technically, the Speaker will claim that the SNP could not form a government across the whole UK, should the Tory government fall. More prosaically, Bercow is a Unionist and a Tory at heart, so giving the SNP official limelight is hardly a real option.

That said, there is a keen awareness at Westminster that the SNP are on their game and able to cause the Tory government damage. With both Tories and Labour utterly divided on any post-Brexit strategy, the SNP will dominate the Commons over the new parliamentary session.

I can’t wait to get started.