Now that the UK general election campaign is formally under way, Boris Johnson has no guarantee if his big gamble will pay off. And if it doesn't, he will be in unfortunate company in the history books. 

A Labour resurgence, a swing to the Lib Dems, or enough Tory votes leaking to the Brexit Party could all undo the British PM's plans to stay the PM. But even if Boris Johnson does lose the Prime Ministership, he'll be spared one humiliation at least.

In Theresa May’s Downing Street, there was a lot of talk about 'Gordon Brown Day'. It was the day on which Mrs May would overtake the former Labour leader in terms of time spent as Prime Minister.

Despite the expectations of many, May got past the milestone and ultimately served 58 days longer in Number 10 than Brown did. It wasn’t perhaps much of an achievement, but Mrs May didn’t have that many achievements in the bank and it was at least something.

I’m not sure if Boris Johnson or his Svengali, Dominic Cummings, has 20 November circled on the calendar. They should, for it is 'George Canning Day' - the day on which Johnson’s time as Prime Minister will outstrip that of Canning, who died in office in 1827 after just 119 days.

George Canning is the shortest-serving British prime minister

This makes Canning the shortest serving British Prime Minister to date. Despite this, there is a large statue of him in Parliament Square, beside Westminster. He had considerable political achievements before gaining the top job, particularly as Foreign Secretary.

Johnson also served as Foreign Secretary, of course, though without any particular achievements to show for it. The two men also share the same educational background, both being products of Eton and Oxford.

Canning’s other claim to fame is having contributed to a bitter split in the Conservative Party, a feat Johnson may yet emulate.

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In any event, with the UK general election set for 12 December, Mr Johnson knows that he will pass 'George Canning Day' and avoid becoming Britain’s shortest serving Prime Minister. He will also outlast Canning’s successor, Viscount Goderich, who only managed 130 days in office because he couldn’t hold on to a majority in the House of Commons.

"So far, the lessons of history appear bad for Boris Johnson"

But, as mentioned above, Boris Johnson is far from assured of an election victory. So even though he’ll last longer than Canning and Goderich, he could still be phoning for a removal van from Downing Street on 13 December. If he does, he will have served just 142 days as Prime Minister – the third shortest tenure in history.

Even if this were to happen, Mr Johnson could take heart from another example from history.

Stanley Baldwin became Prime Minister in May 1923 after the resignation of Andrew Bonar Law (who, with 211 days in office, had the third shortest tenure apart from Johnson).

That December, feeling the need for a personal mandate, Baldwin called a snap election. This was the last time a British election was held in December.

It was also, curiously, fought mainly on a question of trade policy. The issue at the time was tariff reform - Baldwin wanted to introduce tariffs, reversing Britain’s traditional policy of free trade.

The Tories were as split on the tariff question as they are on Brexit, and some suggested holding a referendum on the issue – though as we now know, a referendum doesn’t necessarily resolve issues like this.

And, in echoes of the arguments about 'Project Fear' in recent times, many voters were worried that food prices would rise if Baldwin got his way.

This fear cost the Conservatives votes and Baldwin lost his majority. As a result, James Ramsay MacDonald was able to form a minority Labour government, supported by the Liberals.

So far, the lessons of history appear bad for Boris Johnson. However, MacDonald’s shaky government only lasted ten months and Baldwin returned to office with a majority in October 1924, going on to serve a total of seven years and 82 days as Prime Minister.

Boris Johnson likes to pepper his speeches with historical analogies from Classical times; perhaps he might find food for thought in the lessons of British history.