The price rise will affect 4.1 million customers who will see average bills increase by £60 a year. : British Gas is to increase the energy prices for those on standard tariffs by an average of 5.5% - or £60 a year. The rise, which applies to both gas and electricity, will see the average annual dual-fuel bill go up to £1,161. The company, the UK's largest energy supplier, said that 4.1 million of its customers would be affected.