The biggest outbreak of swine flu in Norfolk so far has erupted at a city business, it was confirmed last night.A number of people who work at the Royal Bank of Scotland Mortgages office in Amsterdam Place have been infected with the H1N1 virus.

The biggest outbreak of swine flu in Norfolk so far has erupted at a city business, it was confirmed last night.

A number of people who work at the Royal Bank of Scotland Mortgages office in Amsterdam Place have been infected with the H1N1 virus.

It is believed up to 40 employees were sent home on Monday afternoon while health bosses gave the company - which employs 250 staff at the site - advice on how to deal with the virus.

At least three people contracted the flu and more than 15 others who sat in close proximity to the people infected were given anti-viral drug Tamiflu.

RBS bosses said the people who contracted the virus were not in direct contact with members of the public and actions are in place to prevent further cases. The bank would not confirm exactly how many people were affected but said it was a 'small number'.

So far there have been isolated cases in the county but the latest outbreak at RBS is the largest number of cases in one place which have been reported.

Meanwhile three more Norfolk schools have been hit with swine flu. It is suspected that one member of staff and one pupil has the virus at Stalham High School in Brumstead Road, Stalham.

There is also a suspected outbreak at Northgate School in Yarmouth and St Nicholas School, also in Yarmouth.

A spokesman for RBS said: 'The affected individuals were not dealing with members of the public and are receiving the appropriate treatment. We have moved quickly to ensure that any risk to staff is minimised.

On July 2 guidelines changed on how the virus was dealt with due to the increase in cases. The Department of Health and the Health Protection Agency issued guidance about swine flu no longer needing to be confirmed by laboratory testing.

It means the number of confirmed cases is hard to identify with many people in workplaces or schools displaying symptoms of the virus but who have not necessarily been tested.

GPs in NHS Norfolk and NHS Great Yarmouth and Waveney are now diagnosing swine flu based on clinical symptoms rather than awaiting laboratory test results.

Following diagnosis GPs can arrange for their patients to receive antiviral drugs if it is considered clinically appropriate. As a result it will no longer be necessary to confirm each new case of swine flu by laboratory testing.