This general election campaign is set to be an epochal, history-making election whichever way it goes.

If Starmer wins an outright majority, it will be the largest ever uniform swing for a winning party, beyond what Tony Blair achieved in 1997. If Rishi Sunak manages to remain in Downing Street – well no PM has ever come back from being 20 points behind in the polls six months out from an election, let alone weeks.

So either way, July 4 will be a record-breaking battle for No.10.

It was, I understand, a “finely balanced” decision to call the election. The prime minister had been taking soundings from colleagues. He had called the civil service in last week to advise on timing options.

I hear from a couple of sources that Isaac Levido, Sunak’s campaign chief, had wanted to go in the autumn, in order to test the messages and see economic improvement bed in, but the PM decided to go now.

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One person who knows the PM explained it to me as this – the PM wants to project confidence and believes he has a plan for the country that aligns with voters. One No.10 source told me Michael Gove summed up it best in cabinet: “Who dares wins and you dare and you are going to win.”

For Labour, euphoria. For the Tories a show of strength

But to get a sense check as we kick off day one of the campaign, let me give you a taster of the mood in the different camps.

On the Labour side, euphoria; they get the election they have been calling for, at a moment when some around Starmer would quietly say to you that the only way is down in terms of polling. Months of trying to hold the lead turns to weeks. And the message is singular: “Change, that’s our election message.”

On the Tory side, Sunak’s allies explain it like this; the economy is back to normal and this is a “show of strength” to quote one. “He’s not afraid and is completely and utterly confident in his values and principles being aligned with the public and being able to prosecute that argument.”

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Choice or change

There is, I think, something else at play. Some 10 months of wage growth while inflation has been falling hasn’t reaped the dividends with voters that perhaps Team Sunak expected. People aren’t feeling the difference, and waiting a few months isn’t going to change that. So with good economic news now – on inflation and growth – the PM sets it up as a choice.

His MPs are spitting as they look down the barrel of election loss – whatever the gloss Mr Gove likes to put on it. I’m told that a sitting minister publicly asked at the meeting of backbench MPs on Wednesday night if they could submit a letter of no confidence in the PM. “It’s madness,” said one former cabinet minister on election timing, while another told me: “We are in deep trouble.”

As for the coming weeks, get used to these messages: Sunak on the choice at the next election and Starmer on the change.

Labour believe that the voters have had enough of the Conservatives, and this has been borne out in recent ballot box tests. Mr Sunak has made the gamble he can pull off in six weeks what he has failed to do 18 months into the job – win voters over.

Starmer win, or Sunak comeback of the century? Either way 4 July will be a record-breaking battle for No.10.