Prime Minister Gordon Brown said on Tuesday that Britain is one of the best prepared countries to deal with swine flu and "all action necessary" will be taken to stop its spread.

"I understand the very real concern that people have in Britain and across the world. Let me reassure you that we have been preparing for this kind of scenario for many years," Brown said.

The prime minister said the two confirmed cases are believed in better health and one may even leave hospital later on Tuesday.

The British government called a meeting of its emergency committee COBRA (Cabinet Office Brief Room A), while the Foreign Office advises against non-essential travel to Mexico.

The Foreign Office said in a statement on its website that travelers should consult a doctor immediately if they show signs of flu-like symptoms.

"British nationals should continue to follow local advice on precautions to take to avoid exposure to the influenza," the statement said.

Health Secretary Alan Johnson said there are 14 suspected cases being investigated in Britain, all of whom are well enough to be managed in the community.

The World Health Organization has raised its alert level to four -- two steps short of declaring a pandemic. Level four means the virus is showing a sustained ability to pass from human to human, and is able to cause community-level outbreaks.

Swine flu is a respiratory disease thought to spread through coughing and sneezing like normal flu. More than 150 people are thought to have died from the disease.