Nine new cases of swine flu have been confirmed in the UK, taking the total to 27. The sudden surge in cases came after the Government urged the public to remain on the alert, and warned a second wave of the deadly virus could hit Britain in the coming months. Environment Secretary Hilary Benn said the flu is "relatively mild and responds well to treatment here in the UK so far but we have got to remain vigilant". "It's best to play safe in relation to this. We are still not absolutely sure what it is that we are dealing with. The truth is we just don't know," he said. He said the outbreak was still "relatively small" and Britain is well prepared but that the "biggest worry" is that the H1N1 virus could mutate, so what might seem like an over-reaction was "the right thing to do". Health Secretary Alan Johnson said there could be another more serious outbreak in autumn or winter. Alleyn's School, in Dulwich, southeast London, became the fourth school to close after five year seven pupils tested positive for the virus. Two other children confirmed as having the virus are London-based siblings who are close contacts of a previously confirmed case, the Health Protection Agency said. Two adults from London and the West Midlands, who recently returned from Mexico, have also been diagnosed with swine flu. There have been at least 934 confirmed cases worldwide in Mexico, the US, Canada, Spain, the UK, Germany, New Zealand, Italy, France, Israel, South Korea, Colombia, Costa Rica, Ireland, Switzerland, Austria, Hong Kong, Denmark and Holland. Britain has the second-highest number of swine flu cases in Europe, after 40 confirmed cases in Spain.