An emergency inspection by environmental health officers was under way at food manufacturer Katsouris, with the FSA joining for "moral support and fact-finding", following revelations of food safety breaches at one of its ready meal factories.

It comes after footage aired on the Whistleblower programme showed filthy lavatories at the Ealing factory and employees failing to change their boots before, or wash their hands after using them. They also moved product in buckets plucked from the floor and left finished ready meals standing for hours without chilling.

The news comes just months after salmonella was found in Katsouris' houmous. Its biggest customer is M&S, but it also supplies Sainsbury's and Tesco. The Bakkavör-owned company, with £160m turnover in 2005, said workers were being retrained and would be more closely supervised following the "unacceptable breaches of company policy".

Tesco said it had already carried out a spot check on the plant. A spokesman said: "We're all over Katsouris on its food safety procedures. I know the management will be very disappointed by the lapses, but it's too early to say what action we will take. We need to ensure they address the issues immediately because clearly we won't allow that sort of thing to go on."

A former director at a major multiple said: "No one has a contract with anybody in this business. Things change overnight."