WEDNESDAY should prove a momentous day at Westminster and for the UK. Theresa May will appear for her last Prime Minister’s Questions. Expect lots of obsequious and hypocritical tributes from the Brexiteer Tories. Mrs May’s 40 minutes at PMQs will be followed immediately by a standing ovation from the very Conservative colleagues who knifed her in the front. Presumably, the SNP MPs will sit in their seats.

But the real fun will be taking place at Buckingham Palace where – barring divine intervention – New York-born Alexander Boris de Pfeffel Johnson will be kissing the hand of Mrs Windsor, becoming her 14th prime minister and the third in only three years. An unelected prime minister, the 19th to be educated at Eton, will be anointed by an unelected head of state.

On Wednesday evening, the new PM will address the ranks of Conservative MPs at the backbench 1922 Committee. Desks will be banged, another ritual in the ancient regime that is British politics.

Except that ancient regime is on its last legs. Westminster itself has ground to a halt – the main business in the chamber on Wednesday is the Dockless Bicycles (Regulation) Bill. The British economy is teetering on the edge of disaster, with the Office for Budget Responsibility (the official budget watchdog) predicting a recession and a doubling of public borrowing, if there’s a soft Brexit.

Both major parties are in existential crisis, with neither attracting more than a quarter of the electorate. The latest polling data suggests a hung parliament, with Labour still 52 seats short of a majority. Internationally, Britain is a laughingstock with a Lilliputian navy that can’t protect UK shipping from Iranian rubber boats.

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Much is now resting on the shoulders of BoJo who, if the Sunday papers are to believed, is currently more worried about getting the taxpayer to fund a new bed at 10 Downing Street for himself and the first mistress than he is about saving the nation. But perhaps it is too easy to make light of Boris. True, his premiership is probably the last throw of the dice as far as saving the decrepit British state is concerned. Yet there is something very different about Boris Johnson’s coming premiership: it will be Britain’s first exercise in having a populist prime minister. Will it work?

By populist, I mean that Boris will appeal over the body of Parliament and directly to the “people”. The UK’s non-existent written constitution leaves huge residual executive powers in the hands of the incumbent of Downing Street. Should Boris choose to use those powers, he can rule virtually by decree. And remember, he is the first pro-Brexit prime minister. The lunatics really are about to take charge of the asylum.

Everything is down to how BoJo behaves in his first week in office. Will his establishment (and Classical) training draw him back into the eternal folds of Britain’s ruling, if obsolescent, oligarchy? – the City, landed interests, civil service mandarins, Oxbridge, press barons, corporate lawyers and lobbyists, the Windsor clique.

Or is Boris Johnson brutal enough behind the blond curls to use his ascent to power to affirm the interests of a new, pro-Brexit ruling elite? – hedge fund barrow boys, nouveau riche foreign oligarchs, a rentier class of buy-to-let owners fearful they will be disposed, and a generation of affluent, largely-English middle-class pensioners desperately hiding from the realities of frenetic, 21st-century reality.

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One defining test is the new Cabinet that Boris installs. We already know he needs a new chancellor after Philip Hammond’s rather calculated “on air” resignation on the Andrew Marr Show yesterday. If Boris is really up for a no-deal Brexit on World Trade Organisation rules, he needs a Cabinet that will back him to the hilt. That means around 15 of the present incumbents will be on the backbenches by the weekend, creating a huge group of malcontents for Boris to deal with.

There are already rumours that Boris is asking prospective Cabinet recruits to give written guarantees they will vote for a hard Brexit if demanded. Expect known Brexiteers such as Dominic Raab, Priti Patel, Esther McVey and Andrea Leadsom to return. There is also much leaking that Boris will offer a ceremonial olive branch to Michael Gove, former friend turned rival.

There’s only one problem with this approach – it risks splitting the Conservative Party definitively, if it drives Remainers such as Hammond into a corner. Boris might balk at being the man who destroyed the Tory party. On past record, he is more of a fudger than Donald

Trump or Nigel Farage. Yet if he is serious about driving through a hard Brexit – which must entail, at some point, a General Election – he has to crush his Remainer wets. Farage was prepared to dump Ukip and start a new party in order to exercise control. My gut feeling is that self-indulgent Boris lacks this killer instinct.

The same can’t be said for his henchmen. The oily and over-ambitious Gavin Williamson, fired by Mrs May for allegedly leaking National Security Council decisions to the Daily Telegraph, has been Johnson’s campaign manager and chief arm-twister. Steve Baker,

chief ideologue of the European Research Group of Tory MPs, could be Brexit Secretary under Johnson. These men take no prisoners.

Which is why Boris in Downing Street is not the same as Boris when London mayor.

Yet BoJo has one ace up his sleeve when it comes to holding the Tory party together: he’s no fiscal conservative. As shown by his daily announcements of new spending commitments during the internal hustings for the Tory leadership, Boris does not care how much he spends. He promised £5 billion for English schools, £9bn to raise the higher-rate threshold for income tax, £1bn for more police in England, an estimated £34.5bn to put full-fibre broadband in every home by 2025, plus a lot more. That might be enough to win over enough Tory Remainers to get Brexit through.

Boris is a consummate political showman. He will have precisely 99 days between becoming PM and the fateful Halloween deadline for Brexit. I think he might accept a soft Brexit deal, if offered by the EU; claim a diplomatic victory whatever the truth; then go for an instant election. With Corbyn’s Labour Party imploding over anti-Semitism claims, BoJo could win the most seats, though I doubt if even he could secure a majority. In which case, we are locked in a war of permanent parliamentary manoeuvre. Scotland will have to take bold steps if it wants to extricate itself from the UK.

Alternatively, if a combination of Boris’s synthetic charm and the political thuggery of Gavin Williamson and Steve Baker don’t win enough Tories round,

then we may well see a General Election in September.

Expect a flurry of juicy spending commitments in the next few weeks and a high-profile visit to Washington, just in case. Even then, a quick election probably favours the anti-Brexit parties. In which case Boris enters the record books as the shortest-serving PM on record.

But one thing we should not do is underestimate Boris de Pfeffel Johnson. On Wednesday he achieves his life’s ambition: power. He won’t give it up without a fight.