Npower has outsourced the printing and mailing of customer bills and statements to the Leicester-based company since 2000.

A statement from Opus Trust Marketing said future plans for Npower included new communications designs that would take advantage of its investment in high-speed digital print technology to present clearer customer communications.

Opus Trust Marketing chief executive Linda Scott would not confirm exactly how much the contract was worth, but said it had significantly grown since 2006, when it was worth £500,000, and it was now a multi-million pound contract.

She said the main development since Opus Trust Marketing first took on the contract in 2000 had been taking the Npower documents to colour.

"And it’s not just been about using colour for colour’s sake, but using it to help the consumer understand the document better," she said. She added that transpromo was "not a big thing" in the utility market, but that the focus was on making documents more user-friendly.

Scott said that over the next three years Opus Trust Marketing would be looking to innovate further for Npower, and in particular was focusing on more of a multi-channel offering for the consumer.

Npower marketing operations manager Hilary O’Grady said: "After a comprehensive review where price, quality and innovation were all put under the microscope, we have found that Opus Trust Marketing continues to offer the best solution."