Under the deal, Axpo will provide So Energy with access to short and long-term commodity markets and improve the company's access to renewable energy sources.

The deal also strengthens Axpo's presence in the British energy market, the firm said. Financial details of the deal were not disclosed.

Axpo is Switzerland's largest producer of renewable energy and is involved in energy trading and marketing solar and wind power. So Energy supplies renewable electricity and gas to around 200,000 homes in England, Wales and Scotland.

(Reporting by Nina Chestney; Editing by Alex Richardson)