Health officials have now confirmed 21 cases of the virus and it is feared that the number could double as more blood tests are analysed.
The outbreak was first revealed in The Independent in February when three patients fell ill. All 21 victims had attended an alternative medicine centre in north London and were given a treatment called haemotherapy.
The unorthodox treatment involves injecting the patients' blood, mixed with other solutions, back into their body through acupuncture points in their toes, knees, heads and elsewhere.
The Finchley Alternative Medical Centre has agreed to stop the controversial treatment while an investigation is carried out by Barnet Health Authority into the cause of the outbreak. Inquiries are also being made by the Health and Safety Executive.
Patients came to the centre from all over the country and medical records show that 219 people were given haemotherapy. They have all been asked to supply blood for testing at the Public Health Laboratory Service Communicable Diseases Surveillance Centre in London. This weekend a Barnet Health Authority spokeswoman said: "We have 21 confirmed cases so far. Over 100 tests are still to come in and roughly one in six are coming back positive."
Many of the victims are being treated by Professor Geoffrey Duscheiko, a liver specialist at the Royal Free Hospital in north-west London. Professor Duscheiko said that the outbreak was highly unusual both in scale and because many patients were still incubating the virus.
"They are all at various stages of hepatitis, but fortunately none of them are in a life-threatening situation," he said. "They will need careful watching as so many of them are in an early stage."
It is feared that many people could be incubating hepatitis B with no knowledge that they have the virus, which can be passed on to sexual partners without the carrier having any symptoms. Barnet health officials believe it is one of the worst outbreaks of hepatitis in Britain for 50 years.
One of the victims, Fred Canty, a sales representative from Enfield in Middlesex, had visited the medical centre looking for treatment for an allergy which caused his tongue to swell up. Mr Canty, who was attracted to the centre last October by an advertisement in Yellow Pages, was given four treatments of haemotherapy.
"The doctor would fill a syringe with half an inch of my blood. Then he would mix it with fluids and serums. He injected it between my toes, between my thumb and index finger, in my trapezius muscle, and under my scalp; in all the acupuncture points," he said.
On 25 January, Mr Canty, 60, fell ill with a high fever. His doctor gave him blood tests and detected jaundice before referring him to Chase Farm Hospital in Enfield, where he was diagnosed with hepatitis. He is now considering legal action against the centre.