Winner Helen Morgan overturned a Tory majority of almost 23,000, declaring that the “party is over” for the PM.

The result follows a torrid week for Mr Johnson, who has faced criticism over Downing Street parties and a rebellion by his own MPs over Covid measures.

Tory MP Sir Roger Gale said the prime minister was on “last orders”.

“One more strike and he’s out,” he told BBC Radio 4’s Today programme, adding that the by-election “has to be seen as a referendum on the prime minister’s performance”.

Conservative Party chairman Oliver Dowden said: “I know that the voters of North Shropshire are fed up and they wanted to give us a kicking… We’ve heard that message loud and clear.”

But he added: “I don’t think this amounts to a sea-change.”

The by-election followed the resignation of Owen Paterson, the MP for North Shropshire since 1997, who was found to have breached parliamentary rules on lobbying.