The prime minister may be out of the UK for eight days as he embarks on a diplomatic tour taking in a triumvirate of summits – CHOGM, the G7 and NATO – but he cannot escape the enormity of what’s happening back home in his first ballot box test since this month’s confidence vote in his leadership.

These by-elections are particularly instructive because they cut across two electoral battlegrounds for Boris Johnson.

Wakefield is in his bank of Red Wall seats taken from Labour in 2019.

Tiverton and Honiton is in true blue Devon, the rural Blue Wall of the South West, where the Lib Dems are hoping to take what should be an ultra-safe seat from the Tories.

Follow live updates on a nervy night for Boris Johnson in two by-elections

In Wakefield, Labour are quietly confident of winning back this West Yorkshire seat lost to the Tories in 2019, while in Tiverton, Lib Dems are hopeful that they can “climb a mountain” to win – providing they can turn out their vote.

Losing both seats will be deeply uncomfortable for Mr Johnson.

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The last time the Conservatives lost two by-election seats on one day was in 1991 (although the party went on to win back those constituencies in the 1992 general election).

But this would be a record-breaking moment if both seats do fall, because it would mean the Lib Dems had overturned a 51.5% Tory majority – the biggest percentage Tory majority ever overturned in a by-election.

Asked about whether he’d consider his position if he lost both seats, the prime minister looked aghast.

“Are you crazy?” he replied to reporters, as he sought to downplay the importance of these two by-elections.

Mr Johnson brushed aside questions that his popularity had been badly damaged by partygate and the subsequent confidence vote, pointing out it was only a year ago that he defied all the odds with a historic win in Hartlepool.

But he also sought to dampen expectations, telling reporters as he landed in Kigali, Rwanda, that while he was “always full of optimism and buoyancy”, political observers knew only too well that “by-elections in midterm are never necessarily easy for any government”.

But a double loss will rattle his already anxious party, as MPs in marginal seats ask themselves again whether the fallout from Mr Johnson’s conduct might cost them their jobs in a general election.

It all feeds into the narrative that the prime minister is potentially fatally wounded after partygate and won’t be able to win the public back around.

But for all that, even his opponents quietly acknowledge that these losses don’t pose an immediate existential threat.

Two former cabinet ministers told me this week that the defeats are baked in, while his success in the recent Conservative MPs’ confidence vote makes it very hard to agitate to dislodge Mr Johnson for some months yet.

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For Labour, winning Wakefield is a necessity if the party is to have any hope of repairing the damage of 2019 and retaking seats it will need to have any hope of taking power at the next general election. This is Sir Keir Starmer’s 38th target seat, requiring a 3.7% swing on current boundaries, so well in reach.

For the Lib Dems, taking Tiverton would quite simply be a political earthquake that will give the party belief that it is once more turning into a serious electoral force following its post-coalition routing in the 2015 general election. Tiverton is the Lib Dems 167th target seat and requires a 20.3% swing on current boundaries.

And for the prime minister, losing these two seats would still leave his government with a working majority of 75 MPs.

What he can’t entirely count on any more is their loyalty and support in pushing his programme for government through parliament. The vote may have reached a conclusion, but the internal civil war is far from resolved, and ballot boxes will only add to the pressure on a prime minister suffering more than just midterm blues.

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