British Sugar intends to invest substantially more than �25m in a biogas plant to cut fossil fuel use by a quarter at its flagship Wissington factory.

A proposed bioenergy plant at the world's largest beet sugar factory, near Downham Market, would make methane gas to power operations on the 500-acre site.

It will create 10 new jobs and about 200 in the construction phase, which should start early next year if approved by Norfolk County Council.

The 'beet biogas' production would be enough to heat about 22,000 homes and would cut Wissington's carbon dioxide emissions by about 90,000 tonnes a year.

Factory manager Paul Hitchcock said: 'One of the good things about this project is we can start to say that we're growing our own fuel.'

Wissington makes sugar from more than two million tonnes of beet grown by the region's farmers. It also markets a valued by-product of about 150,000 tonnes of dried, pelleted beet pulp for feeding to livestock.

Converting the pulp into 'beet biogas' would achieve further major cuts in fossil fuel use, said Mr Hitchcock.

After extracting sugar, about 100,000 tonnes of pulp will feed an anaerobic digestion plant on the edge of the site. The process creates water, which will be treated before discharge, and solids, which will be dried as a fertiliser for farmers. It also produces gas, roughly 50:50 methane and carbon dioxide, which will be taken from the lagoon and pumped into the boilerhouse for electricity generation.

'We're balancing the cost of fuel with cost benefit of animal feed. This is the most critical financial balance of this project because we will lose revenue from selling animal feed,' said Mr Hitchcock.

The covered lagoon, which will contain about 150,000 cubic metres, should produce about 12.5 million therms of gas, or 25pc of the factory's power needs, from summer 2013.

The lagoon, which will be lined with clay and a plastic membrane, will be sunk five metres below ground and be five metres high.

Mr Hitchcock, who has a total of 267 permanent staff, said: 'We've been running a pilot plant on site, which we have been feeding with pressed pulp from the 2009/10 campaign. And over the past year we've gathered a lot of data about how we can get best yields.'

There will be public exhibitions on July 2, at Southery village hall, 9am to noon, and at Downham Market Town Hall, 1.30pm to 5pm. The exhibition will also be at Wereham village hall on Monday, July 4, 4pm to 7pm.