BBC Europe correspondent Colin Blane: "The report comes at an embarrassing time for the French government"

The French authorities have 15 days to come up with suggestions to supervise rendering plants, which boil bones and other waste from slaughtered animals which is then sold on to animal feed makers.

The commission launched its investigation in August after French media reports that animal feed had been contaminated with dangerous pesticides, heavy metals and human waste.

'Deficiencies'

A report published by the investigating scientists on Friday revealed how they monitored controls on sewage sludge at rendering plants and studied the use of sludge collected from waste water disposal systems.

The report says: "The mission identified deficiencies in the prohibition of certain substances in the production of feeding stuff.

"Certain plants in the French rendering industry have used for years prohibited substances such as sludge from the biological treatment of the waste water or water from septic tanks from their own establishments or, possibly, from their suppliers."

France argues that since the waste is being heat treated, the resulting matter is safe and can no longer be considered sewage sludge. The Commission strongly disagrees.

The report says: "It is still not fully clear if and how the French authorities controlled the segregation between human waste and industrial waste in the waste water disposal system and the subsequent recycling by the rendering plants."

The report's findings come at an embarrassing time for the French Government, which has been threatened with legal action by the commission over its refusal to allow the sale of British beef on the grounds that it may still constitute a health risk.

Conservatives in the UK are now demanding a ban on the import of French meat.