The number of people switching energy supplier has leapt by 30% in a year as consumers vote with their feet following high-profile price hikes.

Just under 445,000 customers switched electricity supplier last month, compared with the 342,000 who moved in August 2016, taking the total number of customers switching so far in 2017 to almost 3.5 million, according to Energy UK, which represents suppliers.

Britain’s biggest energy supplier, British Gas, is increasing its electricity prices by 12.5% in a move affecting 3.1 million customers from Friday. The increase means the company’s average annual dual-fuel bill will rise by 7.3%, or £76, to £1,120.

The price comparison site uSwitch.com said: “The sheer number of people who switched in August is clear evidence that customers are not taking price hikes lying down.”

However Energy UK said the figures suggested that “progress is being made” following concern in some quarters about the millions of people sitting on poor-value standard variable tariffs. Theresa May had pledged to impose a price cap to address the “injustice” of families collectively paying £1.4bn over the odds.

There are now more than 50 energy companies vying for people’s custom and almost a quarter of all last month’s switches involved people moving to small and medium-sized suppliers from the larger players.

According to uSwitch, at least 10% of people who switched energy supplier for both gas and electricity between June and November 2016 saved £618 or more.

Campaigners have called on the government to do more. The prime minister had pledged a price cap on energy bills for 17m families during the general election campaign but the policy was missing from the Queen’s speech.

At a private meeting in late August, the energy regulator Ofgem told the big six energy suppliers and dozens of challenger companies that it was planning a price cap for 2 million people. The cap would apply to vulnerable customers who are eligible for the warm home discount scheme. While full details are due to be outlined later this month, the cap is expected to be introduced in January, sooner than expected, so that hard-pressed consumers receive relief during the winter months.

In the Commons on Tuesday the business secretary, Greg Clark, said he expected the energy regulator to “do [its] job and stand up for consumers” by curbing prices.

MPs heard that Ofgem had yet formally to respond to the government’s letter, sent in June, which asked for details on how the regulator would act to protect customers on the poorest-value tariffs. Clark said he believed it would be “excessive” to compel Ofgem to implement an energy price cap, adding that “the ball is in their court”.

Meanwhile one of the newest arrivals to the sector, Fischer Energy, claimed the government should open an inquiry into whether people on standard variable tariffs should receive refunds if they have been overpaying.

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