The UK energy supplier acquired by Royal Dutch Shell as a vehicle for growth has lost tens of thousands of customers since agreeing the deal.

First Utility supplied gas and electricity to 805,000 UK households when it agreed in December to be taken over by the Anglo-Dutch energy giant, which said it would use it to challenge the Big Six suppliers.

Its UK energy customer numbers have since fallen to 750,000, a drop of 7 per cent, as it faces competition from cut-price start-ups that it claims are unsustainably cheap. It also has customer service issues.

The decline continues a trend that means First Utility has now lost almost a fifth of its UK energy customers since a peak of 920,000 households in mid-2016.