Marks and Spencer and npower have signed the UK retail sector's biggest renewable energy contract.

The six-year deal will see npower provide M&S with 2.6 TWh of renewable electricity from April 2009, enough to power all of the retailer's stores and offices in England and Wales.

Under the landmark contract, npower will supply M&S with electricity from its portfolio of renewable sources, which includes wind and hydro farms. The contract also allows for a 'significant' amount of the supply to be purchased directly from independent small-scale generators of renewables.

"Securing this contract with npower is a major achievement for M&S," said Richard Gillies, M&S's sustainability programme, Plan A. "Not only does it significantly move us towards our goal of using 100% renewable electricity across our stores and offices, it also strengthens our market-leading commitment to encouraging small third-party generators, including some of our own suppliers, to develop renewable electricity."

The contract is another step towards M&S's Plan A goal to become carbon neutral through reducing energy usage, sourcing renewable power and using offsetting only as a last resort. From a 2006/07 baseline, M&S said it had reduced its like-for-like electricity consumption by over 6% and sourced over 30% of its electricity from renewables, including five distributed generation sites featuring wind turbines, anaerobic digestion plants and small hydro schemes.

All of M&S's existing renewable energy contracts with small distributed generators will be integrated into the new npower contract when it starts in April.