Organic cucumbers are failing European Union quality standards because they are more curved than normally cultivated ones, frustrated supermarket chiefs complained yesterday.

Asda said its organic range was being denied Class I classification by stringent European rules on curvature.

Organic campaigners at the Soil Association backed the store and said the problem would only get worse as organic food becomes more popular with consumers.

Asda was yesterday writing to EU Agriculture Commissioner Franz Fischler asking for the regulations to be relaxed.

EU rules state that Class I cucumbers must be practically straight, with a maximum arc of 10mm per 10cm of length.

But organic versions of the fruit tend to be less uniform in shape. The supermarket giant claims that despite its cucumbers being of the highest quality, curves of up to 20mm per 10cm are forcing them to be categorised as Class II.

The store chain said the rules on cucumber conventions were a farce after it discovered it could legally circumvent the regulations - by slicing a crooked Class II cucumber in half, then selling each portion as Class I.

Asda produce director Peter Pritchard said: ''As far as our customers are concerned, curly cucumbers taste just as good as straight ones.

''But it's clear that EU red tape needs to catch up with the massive demand for organic fruit and veg.''

Soil Association spokesman Rob Haward said: ''It's ridiculous that slavish adherence to cosmetic perfection is seen as more important than the produce's actual quality.''

But other organic fruit and vegetables were less likely to be affected, he said, adding: ''Cucumbers are a unique example in that technically they are quite difficult to grow the 'correct' shape.''