Coffee lovers are being conned by suppliers fraudulently mixing inferior beans into products labelled 100% Arabica, scientists have learned.

The discovery came to light as a result of British researchers trying out a new and more accurate method of testing coffee quality.

As part of the study, members of the team and collaborators around the world bought samples of coffee on sale at shops and supermarkets.

They found that a tenth of high quality products labelled "100% Arabica" contained significant levels of inferior and cheaper "Robusta" beans.

Arabica coffee trades at twice the price of Robusta because of its superior taste.

Adulteration with Robusta coffee, which is higher yielding and easier to grow, has always been a potential problem.

But finding rogue Robusta in a sample labelled Arabica is not easy, especially after grinding and roasting.

The standard technique detects the fingerprint chemical 16-OMC, which is only found in Robusta coffee, but is costly and takes three days.

This makes large scale surveillance impractical.

The new method takes only 30 minutes and is sensitive enough to detect just 1% Robusta in a blended coffee.

Lead scientist Dr Kate Kemsley, from the Quadram Institute, formerly known as the Institute of Food Research, said: "This is an important milestone for detecting fraud in coffee, as 1% is the generally accepted cut-off between trace contamination, which might be accidental, and more deliberate adulteration for economic gain."

For the study a total of 60 different coffee samples were purchased in consumer countries around the world, including 22 from the UK.

Chris Stemman, executive director of the British Coffee Association, said: "The BCA welcomes the new insights that the Quadrum Institute are able to provide in determining what types of coffee make up specific products on sale.

"This is an important and easily accessible tool that could potentially be applied as an assurance measure along the coffee supply chain, so that authenticity can be checked and validated at all stages from farm to cup.

"Supply chain integrity remains a key priority for the UK coffee industry and we welcome further research that looks into this in further depth. Currently there is no evidence to suggest that these findings have any impact on the vast majority of products that consumers buy and enjoy drinking every day in the UK."