Under the contract, the Leicester company's second-biggest, Optecon will print 72 million items each year for the two firms, which are owned by international energy group RWE.

Products will include electricity, gas and water bills, payment books and payment cards for npower's 6.3 million customers and Thames Water's 13 million.

Optecon managing director Kris Prashad said that the deal "puts us in line to be one of the largest transactional mail companies in the UK, and probably the largest utility transactional mail firm in the country."

The contract, which begins in November, will double Optecon's output for RWE, as it has printed for npower for the last three years.

Prashad said that the expansion of the contract was down to "our emphasis on quality" and "our innovative software which allows us to get mail to the market at great speed."

A particular requirement of the work, which was won from a shortlist of five firms, will be to handle peak periods for Thames Water half-year billing in March and September.

Prashad said that the company had enough existing capacity to handle the rushes and that no further kit would need to be installed.

RWE npower and RWE Thames Water had previously outsourced print requirements to a number of companies.

RWE npower manager, marketing logistics Hilary O'Grady said: "It's more cost effective for us to source print for the whole company from one supplier than several.

"We chose Optecon because we felt they were best able to deal with the work which is extremely complex. They were already working for npower and doing a great job."

Other Optecon clients include Royal Mail, Avis, Paymaster, the Ayrdale NHS Trust and Lloyds TSB.

Story by Josh Brooks