In the UK, a by-election can easily pass unnoticed, but in times of trouble at the heart of government, it can become a red flag that's impossible to ignore.

So it is, at a time when UK prime minister Boris Johnson is struggling to get COVID-19 legislation through parliament, when allegations persist about the conduct of his team behind the doors of Downing Street, then a by-election is the last thing he wanted.

North Shropshire is usually a safe Tory seat. There's been a Conservative MP installed comfortably in this rural constituency for decades.

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The 34 percent swing from Conservative to Liberal Democrat is the second-highest recorded in a by-election between the two parties, only beaten back in 1994.

"I think Conservative MPs will be very alarmed by this result because these were lifelong Conservatives dismayed at Boris Johnson's lack of decency, saying they don't like him, they don't want him," said Liberal Democrat leader Ed Davey. 

That's partly true, but there's also another use for by-election disasters, and that's to fire a warning shot.

North Shropshire is a pro-Brexit region of England, older working-class voters who backed Johnson to take the UK out of Europe.

It's not the kind of area that would normally side with the Liberal Democrats and perhaps were the stakes higher in a national election the result could have been different.

Previous Prime Ministers have lost by-elections and gone on to win general elections but John Custice, professor at Strathclyde University John Curtice says Johnson should be concerned.

Speaking on Global Business Curtice said Johnson has lost the public trust, "Here is a Prime Minister who is focused on getting things done and isn't too careful about following the rules on getting there."

Johnson takes 'personal responsibility' 

Speaking to broadcasters, Johnson said: "I am responsible for everything the government does and of course I take personal responsibility.

"Clearly the vote in North Shropshire is a very disappointing result and I totally understand people's frustrations, I hear what the voters are saying in North Shropshire and in all humility I have got to accept that verdict."

Of course, Johnson still has his large majority, and he's proved himself a winner on the national stage, so he's no pushover.

But after the removal of his predecessors David Cameron and Theresa May, the public is getting used to how the Conservative party does business to ensure its survival.

And there are weaknesses in his camp. Johnson is not a traditional politician; he came to parliament from journalism via being mayor of London.

That makes him the new kid on the block in British politics and possibly short on trusted friends.

And it's also worth remembering that the voters of North Shropshire are his support group, Tory voting Brexit supporters. In a game where friends can be everything, he doesn't want to upset those who put him where he is in the first place.