A water company has been told to improve after a huge rise in complaints.

Essex and Suffolk Water will now have to regularly report to its industry watchdog about steps it is taking to get back on track after the number of written complaints about the firm doubled.

It also saw a 28% increase in the number of customers calling with complaints, making it the second worst performing company in England and Wales for complaints about biling and charges.

In particular, the Consumer Council for Water (CCWater) said customers were left frustrated by changes to bills, longer waiting times to deal with issues and abandoned calls.

However the company said that while the figures were "disapponting", it believes they "reflect a very temporary setback while we've implemented new systems".

Professor Bernard Crump, central and eastern chairman of the CCWater, said: "The company struggled to cope with the extra contact that was generated by its new billing system, which caused a lot of frustration for some customers.

"We hope Essex and Suffolk Water is now over the worst of it but we want to see clear evidence over the coming months that complaints are falling and customers are seeing real benefits from the changes to billing."

Claire Sharp, customer director at Northumbrian Water Group, of which Essex and Suffolk is a subsidiary, said: "The figures are disappointing, however we are confident these results reflect a very temporary setback while we've implemented new systems.

"Last year we invested £36million to replace old technology, which had been in place for over two decades, with a major new customer service system.

"Moving forward this will let our customers experience easy, quick and straight forward services, something we know is important to them.

"We'll keep working with CCWater, whom we regularly share our improvement plans with.

"All the signs are positive and I'm very confident the complaints reductions we are seeing are lasting and will continue.

"The investment we've made in new technology will make sure in the long term we continue to provide unrivalled customer service for our customers."