E.ON is the fourth energy company to announce a hike to its gas and electricity prices in the UK. Its electricity prices will rise by 11.4 per cent and gas costs will be up 18.1% from next month. E.ON has around five million customers but said almost 600,000 were unaffected by the rise, including its most vulnerable customers on WarmAssist tariffs. It has also guaranteed no more price increases for Age UK customers for at least a year.