Most of the people contacting doctors with concerns about swine flu do not actually have the virus, according to a public health expert.

The director of public health at NHS South Gloucestershire, Dr Chris Payne, said only a small number of people who have come forward with symptoms are being given prescriptions for antiviral drugs.

He said GP services in the area have been very busy with calls, but a lot of people had not actually had swine flu.

The Government set up a national service yesterday afternoon to diagnose patients by telephone or internet and provide them with details of where they can pick up their antiviral drugs.

It is hoped it will take the pressure off GPs, who have been inundated with calls from people with flu-like symptoms.

The Department of Health said there had been a further 100,000 new cases of swine flu reported in England in the last week and 840 patients were in hospital with the virus, 63 in intensive care.

But Dr Payne said: "We are dealing with a lot of anxious people but the actual numbers of people with swine flu are quite low.

"GPs are very busy. They are getting a lot of calls and that is obviously the prime purpose of the new telephone and internet service, to take that load off."

The majority of patients who suffer flu-like symptoms are being advised to contact the flu helpline or visit the internet in the first instance.

If they are found to be suffering with the virus, people will be given a unique reference number so they can arrange for a friend to pick up their Tamiflu or Relenza from a community pharmacies or antiviral centres in the Bristol area.

Women who are pregnant, people with a serious underlying illness or those with a sick child under the age of one should contact their GP if they suffer flu-like symptoms, as should those whose condition suddenly gets much worse or is still getting worse after seven days, or five for a child.

Health experts in the area said they were well prepared to deal with swine flu cases as they increased in number.

Antiviral centres have been set up in every primary care trust area and sites have been found to expand the service if needed.

Experts say there is enough stock of the necessary medication in greater Bristol.

Dr Payne said: "Flu is building up steadily but we are well-prepared for that to continue increasing into August and September. We might get respite and might be lucky with the schools breaking up and people going on holiday and only having their family around them.

"Numbers may decrease and we may get a few weeks or a month or two of it calming down temporarily but all the planning is assuming for the worst. We are planning for the most likely scenario that about 30 per cent of people may become unwell and there is by far an excess of that with stocks for at least 50 per cent of the population."

Liam Williams, the newly appointed project director for pandemic flu at NHS Bristol, said that all the primary care trusts in the former Avon area were working together to ensure that swine flu patients have access to medication.

He said: "Demand for antivirals has increased in the last few weeks and we have worked hard to make sure all sites have access to appropriate levels of stock at all times.

"We would like to reassure everybody that we have more than enough antivirals within the health community to meet population needs."

Despite suggestions that schools might not start the new term as planned in September if swine flu cases increase, Bristol City Council said it would be business as usual, and the only reason for pupils being kept at home would be if staff illness caused a shortage of teachers.