The number of swine flu cases in the UK continues to rise, with 27 cases confirmed by the Health Protection Agency.
There are more than 300 cases under investigation by the agency.
Results show that the disease has begun spreading from people who have recently returned from abroad.
In London, two cases are siblings of school age who are close contacts of a previously confirmed cases in a returned traveller to the US.
A further five cases in London all attend one school, which will remain closed for a week as a precautionary measure.
All pupils at the school are being offered antiviral drugs and advised to monitor their health for flu-like symptoms.
The five cases attend the same school as a pupil recently returned from the US, who has already been confirmed with swine flu.
Latest data from the World Health Organisation shows swine flu has now spread to 21 countries and there are 1,124 confirmed cases worldwide.