More than half a million households switched energy suppliers in September, setting a new record for 2018.
The figures, published monthly by industry trade body Energy UK, showed that of 547,660 households changing providers, 42 per cent ditched large energy suppliers for small or mid-tier alternatives.
Over a quarter switched between large providers and just 11 per cent left smaller suppliers for one of the big names, while a fifth of those surveyed sought to cut costs by switching between small and medium suppliers.
September's numbers brought switching activity to 4m households so far in 2018, a six per cent increase on the same period last year.
However, energy regulator Ofgem's plan to cap energy prices at £1,136 by the end of the year, saving 11m households around £75, could prevent households from switching and achieving greater savings, experts feared.
Lawrence Slade, chief executive of Energy UK, said: “With the proposed price cap expected to be in place by the end of the year it is crucial that switching doesn’t suffer, with Ofgem’s own impact assessment suggesting there could be significant impact on switching levels.”
Stephen Murray, energy expert at Money Super Market, warned the price cap could deliver a "perception of protection" for households, who end up sticking with a supplier on a more expensive tariff.
“However, they may be presented with a shock in Spring 2019, as the price cap level seems destined to rise sharply and leave those millions of customers with increased bills when they could have switched, fixed and relaxed," Murray added.