Boris Johnson has hinted at a ban on fracking, as he moves to shut down controversies that could backfire on the Conservatives in the general election campaign.

An announcement will be made “shortly”, the prime minister told MPs – after acknowledging that the public had “legitimate anxieties” about the earthquakes that are triggered.

No 10 refused to expand on the comments, but green campaigners seized on them to express hope that the Tories were poised to bow to pressure to outlaw fracking altogether.

“If he finally plucks up the courage to ban this dirty industry he will be doing the right thing, just 10 years too late,” said Caroline Lucas, the Green MP.

And Greenpeace said: “If the government has read the science, listened to the huge public opposition and decided to pull the plug on fracking then that should be really welcomed.”

If Mr Johnson does announce a ban, it would represent a remarkable turnaround for a party that pushed for looser rules in order to expand fracking only one year ago.

A leaked letter from then-energy minister Claire Perry argued the current rules for issuing alerts for seismic activity were too “cautious”.

“As we gain experience in applying these measures, the trigger levels can be adjusted upwards without compromising the effectiveness of the controls,” she argued.

But, in August, the UK’s only fracking site, operated by Cuadrilla, near Blackpool, was hit by the largest-ever tremor caused by the practice on British soil.

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The 2.23-magnitude tremor had a depth of 2km (1.2 miles) and was felt by residents in areas including Great Plumpton, Blackpool and Lytham St Annes.

Some Conservative candidates have warned party bosses that support for fracking will be a significant vote-loser, as fears about climate change rise up the political agenda.

Mr Johnson has already moved to shut down a similar controversy – over building the HS2 high-speed rail line – by announcing a review and hinting it will be scaled back.

In the Commons, Alan Whitehead, a Labour MP, said: “Labour will produce a strong offer at the forthcoming election on the climate emergency and net zero [carbon emissions], including a full ban on the extraction of fossil fuel by fracking.

“What chance does the prime minister think he has of matching that offer, particularly in the light of the news that the Conservative manifesto will be written by a lobbyist for the fracking industry?”

In response, Mr Johnson did not comment on the manifesto controversy, but said: “We will shortly make an announcement about fracking in this country, in view of the considerable anxieties that are legitimately being raised about the earthquakes that have followed various fracking attempts in the UK.