The cleaning and disinfecting at a turkey farm hit by bird flu was completed today, but it could be many weeks before it can start operating again.

The cleaning and disinfecting at a turkey farm hit by bird flu was completed today, but it could be many weeks before it can start operating again.

A stringent cleaning process has been carried out at the Bernard Matthews farm at Holton, near Halesworth, where 2,500 turkeys died of bird flu last week. All 160,000 birds on the farm had been killed by Monday and the three-day clean-up has been completed quicker than expected.

Today Defra, the government department dealing with the outbreak, said that reopening the farm could depend on the outcome of the investigation into the cause of the infection - which may never be known.

A spokesman said: “We don't know yet. That depends on when the farm is declared to be disease free and how the outbreak occurred. It is too early to say.”

Yesterday two further farm workers were given the all-clear from bird flu. One vet, Gordon Young from the State Veterinary Service, had already tested negative for bird flu and seasonal flu after developing a respiratory illness. On Wednesday a Portuguese farm worker was taken into the James Paget Hospital in Gorleston for tests, which proved negative today. A third person was also tested today and cleared of any serious illness.

Nick Coveney, director of nursing and patient services said: “The Health Protection Agency has confirmed that tests for avian flu on the patient admitted to the James Paget University Hospital yesterday were negative. This patient will now be treated under normal clinical care.”

A spokesman for the Health Protection Agency, which is in charge of public health, said that no-one was expected to develop the illness because precautions had been taken.

“It's the time of year when people are getting colds and viruses. Anyone with those symptoms who has been at the farm is likely to be concerned. It's probably inevitable that more people will report illnesses.”

A ban on shooting and using bird scarers has been imposed in the 10km surveillance zone around Holton. Farmers who are suffering from serious crop damage must apply for a licence to shoot pigeons.

But there is some good news for free range poultry keepers, who have been told that they will not lose their status as a result of having to take their birds inside. Environment secretary David Miliband has written to MPs to say that free-range meat and eggs can still be labelled as such as long as they are not taken inside for more than 12 weeks.

But some poultry keepers have yet to obey orders to take their birds inside or keep them isolated from wild birds, which applies to a 2,000 sq km area running up to the A47 and to the A140. A spokesman for Suffolk trading standards said there were “10 or less” poultry keepers within the 10km zone who had failed to take action, and could face having their flocks destroyed.

Food and Rural Affairs Minister Lord Rooker told the House of Lords today that even if the DNA structure of the H5N1 virus involved turned out to be the same as the one involved in the Hungarian outbreak, this would not prove that the British outbreak had originated there.

He said: “At present an enormous amount of laboratory work is going on, checking the movements of people, animals, birds, and lorry movements between various plants.”

In south-east Turkey, bird flu has causes of the deaths of 170 birds. South Africa has now joined the list of countries to ban British poultry, which includes Russia, Japan, Ukraine and Hong Kong.