The forces that saw the Liberal Democrats rout the Conservatives in Chesham and Amersham on Thursday could be replicated across other Blue Wall seats in the South of England, Telegraph analysis shows.

Boris Johnson on Friday rejected the “bizarre” idea that the result was a bellwether for the fate of the Tories in their traditional strongholds and accused critics of “misunderstanding” unpopular plans to build more homes under the Government’s planning reforms.

Amersham election historical results

But experts have suggested the 25-point swing could actually represent a “swallow that heralds the summer” for opposition parties looking to disrupt the Tory vote in the South West.

Last month’s local elections saw the Tories take a beating on councils in the South East, losing 34 seats across the region. In the West Midlands and Yorkshire, which are typically Labour-supporting, the party gained 80 and 47 seats respectively.

Labour sources on Friday played up the influence of local factors in the Chesham and Amersham result, pointing to voters’ strong objections to HS2 and planning reforms that many believe will see more homes built on the green belt.

Chesham and Amersham majorities by election year

Many of the green belt constituencies that face disruption from HS2 also contain local authorities where support for the Conservatives fell dramatically last month.

Tories fear that as Mr Johnson focuses on his agenda to “level up” the North of England, traditional Tory seats in the South will feel left behind by the Conservatives.

Bob Seely, the Conservative MP for the Isle of Wight, said the Government’s “standard method” for allocating land for new build housing was “failing to share wealth around”.

Conservatives only lost councillors in the South East

Martin Baxter, of the political analysis firm Electoral Calculus, said that while by-election swings are often driven by local political grievances, they can suggest a “decay” in support for incumbent parties.

“I have never found by-elections to be a good guide to predict future national outcomes, and they are driven by the special factors of the by-elections at the time,” he said.

“But the Liberal Democrats are quite good at holding onto particular by-election wins once they have had them.

Change in councillors in the May 2021 Election compared to the previous election

“When the Government starts to decay, as it were, they begin to lose everywhere, against every party for many reasons.

“This is really the first electoral setback for the Conservatives in a while[…] so this is one swallow.

“I guess the opposition parties will be hoping that more swallows will arrive and herald the summer.”

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