Environmental health officers from 10 boroughs across the country were involved in raids as part of Operation Lobster Pot - an initiative which last year uncovered huge amounts of illegal meat in east London, including decomposing cows' muzzles and goat carcasses. The items were being distributed to high street shops for sale

But the man behind the operation cannot be taken to court because the meat which would have been used as evidence was thrown away following the liquidation of Ciel Logistics, the company paid to store the meat after it had been impounded. The trading standards officers leading the investigation were not told that the meat was being disposed of until it was too late.

All that remains of the investigation is a single prosecution of a high street trader who had received some of the illegal produce.

The mastermind, who cannot be named for legal reasons, cannot be taken to court because he would not have the opportunity to have the meat independently examined. Given the scale of the operation, officers were hoping that he would receive a lengthy prison sentence. He effectively secured his own freedom by going on the run for six months, which stalled the prosecution and meant the meat had to be stored.

Adrian Grieves, principal environmental health officer in Tower Hamlets, London, who led the 18-month investigation, said he and his colleagues were devastated. "As we understand, he was one of the biggest operators out there. We would have prosecuted him for a number of things and we had worked very hard. I contacted Ciel Logistics to say that we wanted to come and have another look at the material, but I found that the phone number had been discontinued."

Paul Greeno, principal lawyer for criminal litigation at Tower Hamlets, said: "These officers spent so much effort and yet, because of the irresponsible actions of a third party, we now have nowhere to go."

Operation Lobster Pot is believed to have cost £500,000.

On the day of the raids, 16 environmental health officers plus trading standards and health and safety officers and police wearing knife-proof vests took part.

Officers found 50 skinned goat carcasses, entrails, rancid chicken, decomposing lambs' brains, cows' heads, smoked cattle hide and cows' feet. Some were infested with maggots. Rat and mouse droppings were also found in the unlicensed meat plant.

It has emerged that the illegal trader had been approaching other firms claiming to be a pet food company requiring cattle and sheep's feet for its recipes. Sometimes he was getting animal parts for free.

Jenny Morris, policy officer of the Chartered Institute for Environmental Health, said: "It can't do anything for the battle against illegal meat. We have now had a number of high profile meat cases that have fallen down. It sends a poor signal to the meat criminals."

A spokesman for the Food Standards Agency said: "After all the time, effort and money spent on this investigation, we are very disappointed.

Ciel Logistics, which was based in Windsor, is understood to have ceased trading in the past few weeks after the withdrawal of its main financial backer. The firm's former managing director, Clive Lawrence, is a high-profile campaigner against the importation of illegal meat through Britain's ports. He advised Heathrow and other airports on ways of stopping illegal imports and warned of the risk to public health caused by the smuggling of African bushmeat. His work was cited during debates in the House of Commons and in the media. Neither he nor anyone from Ciel Logistics could be contacted.

The closure of the firm has also meant the end for the pressure group The Bushmeat Campaign which was mainly funded by Ciel Logistics.