On the face of it, Rishi Sunak’s first Prime Minister’s Questions was an assured performance.

The former chancellor was combative, confident and fluid. But it was also a session in which the new prime minister showed us how conscious he is that his political legitimacy hangs by a thread.

Because being appointed as the UK’s 57th prime minister behind closed doors by 200 or so Conservative MPs will invariably raise questions about his democratic mandate.

That it happened just seven weeks after a different prime minister – Liz Truss – was foisted on the British public by the Conservatives turns those questions into accusations of a democratic stitch-up.

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Labour, the SNP and the Lib Dems all know it, which is why at PMQs they laid into Mr Sunak for being at that despatch box at all.

Sir Keir Starmer accused his new opponent – the third in four months – as someone who was “not on the side of working people” before adding: “That’s why the only time he ran in a competitive election he got trounced by the former prime minister, who herself got beaten by a lettuce.”

He called, again, for a general election.

Mr Sunak however is having none of it, as he teased Sir Keir for backing a second EU referendum – “he talks about mandates, it’s a bit rich coming from the person who tried to overturn the biggest democratic vote in our country’s history” – and spoke again about sticking to the 2019 manifesto.

Sticking to it, because Mr Sunak knows he’s on sticky ground trying to tiptoe into Number 10 and stay there until the next general election in a couple of years asking the British people their view.

That’s why on the steps of Number 10 and in the Commons on Wednesday, Mr Sunak spoke of the Conservative Party mandate won in 2019 as he sought to wrestle that victory squarely from the hands of campaigner-in-chief Boris Johnson.

“I will always be grateful to Boris Johnson for his incredible achievements as prime minister, and I treasure his warmth and generosity of spirit,” he said.

“And I know he would agree that the mandate my party earned in 2019 is not the sole property of any one individual, it is a mandate that belongs to and unites all of us.”

And that manifesto – which Liz Truss sought to deviate from – is now being reinstated by Mr Sunak as he tries to settle his party and cement his ground.

The big move from him on Wednesday was to reinstate the fracking ban, a manifesto commitment from 2019 that Ms Truss sought to reverse and that ultimately became her undoing as she turned a Labour motion on that matter into a confidence vote in her government.

On paper, she won, but the motion triggered her downfall in the chaos that ensued around that vote.

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What’s almost more significant is that in the summer leadership race, Mr Sunak told Sky News that he supported fracking where local people approved of it.

His desire then to row back from this is a sign that he doesn’t want to rock the boat either with Conservative MPs or the public when it comes to testing this mandate.

That has a read across too for the pensions triple lock – the promise to lift pensions by inflation, average wages or 2.5% depending on what’s highest.

An inflation-linked increase would cost the Treasury £5.7bn, according to the Institute for Fiscal Studies (IFS).

But it’s hard to see how on November 17 Mr Sunak does anything but.

He might have fallen out with Boris Johnson, but he’s tied to his predecessor’s plan.

Ms Truss was brought down because she didn’t respect the limit of her mandate.

Mr Sunak knows sticking to it will be his best chance of surviving, not just with his party, but with a thoroughly fed up country too.