Allotment holders in Keighley have been advised to check their plants for the symptoms of contaminated manure.

Marion Pencavel, who chairs the West Yorkshire Organic Group, said she was aware that manure contaminated with a type of herbicide had been used on some allotments in the town.

She said: "A member of the West Yorkshire Organic Group has had a large part of his crop made inedible by the application of some of this manure. The herbicide - called Aminopyralid - is not licensed to be used on food crops. It is spread on grass to kill weeds, the grass is made into hay or silage and fed to animals and it then comes out in their manure."

Lee Senior, the Keighley Town Council allotments officer, said he was only aware of two people on one allotment site in the town who had been affected.

He stressed this was a minor problem relating to one batch of manure and posed no risk to public health. We've looked into it and there's no major problem as far as we're concerned," he said. "It basically just means a few plants have been lost."

He added the contamination was a national issue, which had already come to the attention of the Royal Horticultural Society (RHS).

The herbicide is manufactured by Dow AgroSciences, which has responded to public concerns on its own website.

It states: "We have been receiving inquiries from people who appear to have observed unusual growth patterns in a variety of crops such as potatoes, peas and beans.

"Some callers have inquired whether this may be due to potential herbicide residues in manure.

"Aminopyralid has very little inherent toxicity to people or animals and consumption of affected crops would not have any effect on human health."

Ms Pencavel, who lives in Riddlesden, said vegetables such as potatoes, tomatoes, beans, peas, carrots, aubergines and lettuce seemed to be most susceptible to the herbicide. She said gardeners should look out for distorted leaves and unusual growth patterns. She also recommended such crops should not be eaten.

She said as an additional precaution the crops should be burned instead of composted and the soil in which they were grown rotated and turned over.