BRITISH Gas owner Centrica has suffered its biggest ever one-day shares crash after haemorrhaging 823,000 household energy accounts in four months and warning over full-year earnings.

The FTSE 100 giant saw shares plunge more than 17 per cent at one stage after it revealed the customer exodus at British Gas and said results would also be hit by woes in its North American arm and warmer-than-normal weather in October and November.

It marked its biggest ever intra-day shares fall and took the stock down to levels not seen for 14 years.

The move by British Gas to hike electricity prices by 12.5 per cent in September contributed to the loss of customers between the end of June and end of October.

British Gas – Britain’s biggest energy supplier – now has 13.1 million customer accounts and 7.9 million customers.

All of the UK’s Big Six energy providers have been under pressure from smaller rivals as customers increasingly switch to get the best deal.

The most recent customer losses at British Gas follow 387,000 domestic energy customers shed by the group in the first six months of the year.

Centrica warned its earnings per share would be nearly a fifth lower than expected due to the British Gas woes as well as troubles in its North American arm, which is being hit by “highly competitive market conditions and low price volatility”.

The group said annual earnings in its British Gas business would only break even due to the account losses.