When some of the best-known Conservative figures of the last half-century are booted out of their party, when a new prime minister loses his first parliamentary vote and his governing majority on the same day, when historians are referring to this as a “revolutionary moment”, you know something of great significance is going on. But what exactly is it?

What we are witnessing is another round in the same historic struggle that powered the English civil war of the 17th century: the contest between the executive and the legislature. At its simplest, the House of Commons has voted – once again – to take control of the Brexit process, in order to prevent the UK crashing out of the European Union with no deal on 31 October. That’s the substance of the bill that MPs will vote on, and are likely to pass, today, having cleared the procedural hurdle in dramatic fashion last night. The comparisons with the 17th century are not hyperbolic, because what this move represents is a bid by the legislature – parliament – to grab powers that have traditionally been the preserve of the executive.

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That contest is not over. If MPs succeed today, they will have decided – against the wishes of Boris Johnson – to seek an extension of Britain’s EU membership until 31 January 2020, if no exit agreement has been secured before then.

Johnson has said he will refuse to act on MPs’ wishes, that he will simply not request such an extension from Brussels. To avoid the MPs’ instruction, he would rather empty out the current House of Commons and have a general election to fill a new one, one more sympathetic to his aims. But that can only happen if MPs allow it, by voting for it. Under the current rules, he needs two-thirds of the Commons to agree to an early election and Labour has said it won’t do it – fearing a ruse that would allow Johnson to crash out of the EU during an election campaign.

In other words, parliament is asserting itself and its rights, refusing to be pushed around by an overmighty executive (in the form of Johnson this time, rather than Charles I). Indeed, I’m told that MPs are pondering a means to ensure their will is done over the head of the prime minister: one senior opposition figure has a bill ready that would mandate the Speaker, John Bercow, to apply to Brussels himself for that extension on behalf of the British parliament.

There’s a deep paradox here. It was the champions of Brexit who back in 2016 posed as the defenders of parliamentary sovereignty, determined to reassert the supremacy and independence of the Commons from the supposed encroachments of Brussels. Yet here they are now, fighting parliament at every turn: first proroguing, or suspending, parliament for five weeks; then expelling MPs from their party, even those with decades of devoted service; now seeking to defy parliament’s will. It’s quite a reverse, one captured well by that photograph of the leader of the house, Jacob Rees-Mogg, stretching out contemptuously on the Commons frontbench.

This is not the only revolutionary upheaval under way. Something of that order is currently convulsing the Tory party. A purge that expels two former chancellors and a man who a matter of weeks ago was a candidate for the leadership is an epochal event for the Conservative party. It is changing shape, refashioned by Johnson into the Brexit party by another name – a nationalist, populist party of the hard right.

There is some debate over whether all this – the prorogation, the expulsions – is a series of improvised moves born of panic or, on the contrary, a cunning plan. Within that question is a related one: is the PM’s chief aide, Dominic Cummings, an evil genius or what Marina Hyde calls a “crap svengali”? One of the victims of the Tory purge – Tory grandee and Churchill’s grandson Nicholas Soames – told BBC Newsnight he believes this is all very deliberate. The assumption is that Cummings is intentionally baiting MPs so that he can trigger an election that Johnson will then cast as a populist battle of “people v parliament”.

If that’s right, it is surely the most high-risk electoral strategy ever attempted in this country. It knowingly alienates moderate Tory voters who have always quite liked, say, Ken Clarke, thereby writing off a string of seats – in the south and the West Country – that are likely to fall to the Liberal Democrats. It similarly dooms the Tories in Scotland. So Johnson will begin the next election campaign with that immediate handicap. The Cummings plan is to make up for those lost seats, and gain many more, by winning pro-leave seats in the Midlands and north of England, many of them Labour-held, chiefly by neutralising the Brexit party. Why vote for Nigel Farage when you can get a no-deal, full-monty Brexit with Johnson?

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The trouble with that is, there are plenty of onetime Labour voters who were happy to vote leave in 2016, happy even to vote for Farage in May’s European elections, who may nevertheless balk at voting Tory. Still, Cummings and Johnson are gambling on the belief that they can burn down every other plank of historic Tory support, but win power by delighting the hardcore Brexit base. Win the 35%, enrage everyone else.

A few weeks from now we might be watching a triumphant Johnson returned to Downing Street with a healthy majority, forced to applaud the strategic genius of Dominic Cummings. Or we might marvel that a man who inherited a precarious political situation went on a rampage of revolutionary destruction, thereby making that situation much, much worse.

• Jonathan Freedland is a Guardian columnist