They call it capitalism with a conscience and in Britain it is flourishing. According to new figures, sales of Fairtrade coffee and bananas have doubled in two years with one in five cups of filter coffee drunk in the UK now being supplied from a "fair" source.

The Fairtrade movement, which began life just 18 years ago to protect Mexican coffee farmers against plummeting world prices, has transformed into a global business, with Britain the largest market.

In a written answer to the House of Commons, the trade minister, Ian McCartney, disclosed that the total volume of Fairtrade certified products sold in the UK has grown by 111 per cent since 2003, with total sales reaching £195m in 2005. Sales of Fairtrade coffee in the UK totalled £65.8m last year, up from £34.3m in 2003 while bananas - the third most bought supermarket item after petrol and lottery tickets - rose from £24.3m to £47.7m over the same period. It is estimated that while Fairtrade coffee accounts for just 0.5 per cent of the global market, in the UK the figure is 5 per cent, rising to 20 per cent of premium ground and filter coffee.

As well as the major supermarkets offering their own Fairtrade brands, high street chains such as Costa Coffee, Pret a Manger and Starbucks all now offer ethical alternatives for British consumers.

Fairtrade bananas now account for 8 per cent of the UK market for the nation's favourite fruit.

According to Ian Bretman, the deputy director of the Fairtrade Foundation, the market has been growing by 40 per cent a year for the past five years, and is expected to continue to do so.

"More people are buying it, they are buying more regularly and they are buying more products," he said.

Coffee was the first commodity to be fairly traded and in the meantime - despite global prices remaining stubbornly low - consumers have helped support schools, health and other development projects as well as ensuring small producers retain their livelihood, he said.

However, changes that have been demanded by the World Trade Organisation, implemented by the EU this year, could threaten the future access of some producers, particularly from the Windward Islands, to European markets.

But new products such as wine, flowers and chocolate look set to further boost the annual £200m spent on Fairtrade products in the UK.

Mr McCartney said the Government had contributed £1m to support the Fairtrade initiative in the past five years.