UK co-operative societies grew sales by 4.4% last year to £33bn, according to a ­report to mark the start of Co-operatives Fortnight.

The UK Co-operative Economy Report 2011 also revealed one in five people in the UK are members of a co-operative, with membership increasing by 18% since 2008 to 12.8 million.

Although the largest co-op in the UK by turnover remains The Co-operative Group, it was not the fastest growing society. It was beaten by renewable energy co-op Dulas, which grew sales by 16.1% last year, Edinburgh Bicycle Co-op, which upped sales by 14.7%, and Long Clawson Dairy, which grew by 13.8%.

"The evidence is of remarkably stable growth," said Ed Mayo, secretary general of Co-operatives UK. "Our co-operative economy is in good health still further proof of exactly how economic success can be pursued alongside social responsibility."