Protests against fracking by thousands of people in Sussex over the summer appear to have reversed the growth in British public support for shale gas for the first time.

Polling by the University of Nottingham has shown support for shale gas extraction in the UK steadily rising for more than a year, peaking at 61% in favour in July. But that number fell in September, to 55%.

In August, more than 2,000 people marched against fracking at an oil drilling site run by Cuadrilla near the village of Balcombe, in West Sussex. Dozens of protesters were later arrested, including the Green party MP, Caroline Lucas. They cited concerns over water use by fracking, which involves pumping water and chemicals underground at high pressure to release gas from shale, and said the controversial technique would divert investment away from renewable energy.

Professor Matthew Humphrey from the university's school of political and international relations, who worked on the Nottingham study, said the reverse suggested such high-profile protests could hit public support for fracking: "This may have important implications for the politics of fracking in the UK, if the anti-fracking lobby come to believe that highly visible forms of protest at potential sites for hydraulic fracturing are the most effective means of changing the public mood."

David Cameron said in his party's conference speech on Wednesday that he wanted Blackpool, an area where Cuadrilla has fracked before and says it will be announcing further plans soon, to become "the centre of Europe for the shale gas industry".

The Conservative energy minister, Michael Fallon, also said on Wednesday that up to 40 shale gas wells could be established in the next two years. "I think we're going to see maybe 30, 40 wells drilled over the next couple of years to see what the real potential is - whether this gas can be got out easily as they have been getting it out in the United States and whether they can get it out as cheaply as they have got it out in the United States," he told the BBC.

Friends of the Earth's energy campaigner, Tony Bosworth, said: "With experts saying shale gas won't lead to cheaper fuel bills and scientists warning about the climate impact of fossil fuels, this is not the solution to Britain's energy challenges."

A Guardian poll published this summer found the public were evenly split for and against fracking.