South West Water followed not far behind, with complaints falling by 15 per cent over the 12-month period.

Customers with Wessex Water and Thames Water also showed increasing satisfaction with the service the utilities providers gave, as complaints fell by 13 per cent and nine per cent respectively.

A few competitors fared less well, as United Utilities, Severn Trent, South East Water and Southern all saw their complaint levels rise.

Billing or charging queries were behind 49 per cent of all complaints made to CCW, although the way in which companies handled complaints was another cause.

Watchdog chair Dame Yve Buckland told BBC News it was “disappointing to find some companies, for the second consecutive year, tripping up when they have introduced basic billing systems”.

“In some cases these problems are compounded when customers cannot even reach their company’s staff on the phone to complain,” she added.

Overall, complaints about water companies were at their highest level since 1994, with ten per cent more complaints than in 2005-06.

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