Virulent strains of cold and flu viruses threaten to consign thousands of people to their sickbeds over Christmas and overwhelm the NHS.

More than 300 people per 100,000 are coming down with common colds each week, reports from GPs’ surgeries suggest – a 50 per cent increase on the average for this month.

The sharp increase has coincided with the arrival of the flu virus a month earlier than usual. The outbreaks have also arrived at the peak time for the norovirus – known as the winter vomiting bug.

This year flu-like illnesses, along with common colds and other respiratory infections, are most common among 15 to 44-year-olds, who are rarely offered the flu jab, says the Royal College of General Practitioners. There are about 40 cases of influenza per 100,000 people in England and Wales – the highest December level for eight years.

About 15 million people catch a cold or flu over the winter period in Britain each year. Most seasonal outbreaks of flu occur at the start of the year. Surgeries and hospitals are reporting numbers of cases this month not usually seen until January or February.

Doctors have said that the rise in infections will put hospitals under intense pressure this week as many GPs’ surgeries shut for Christmas.

Updated figures published by the Health Protection Agency (HPA) tomorrow are expected to show worsening flu trends. The agency suggests that this may be because a particular strain of flu, which is known to peak early, is causing up to 90 per cent of the cases.

Those people suffering from minor colds have been told not to expect to see a doctor over Christmas, and instead to contact NHS Direct or walk-in clinics if they are especially concerned, and to call 999 or visit hospitals only in an emergency.

Internet search engines and health websites are also experiencing more inquiries about seasonal illness. Google said that twice as many people in Britain were searching for “flu” this month compared with previous holiday seasons. Its research suggested that this could be the worst outbreak at Christmas for four years, while NHS Direct reported a fourfold rise in flu-related calls over last year.

The flu strain, known as H3N2, is covered by a vaccine against seasonal flu, which is available free to the over65s and others with chronic conditions such as asthma. It was forecast to reemerge this year by the World Health Organisation.

Steve Field, the RCGP’s president and a GP in Birmingham, said that it was worrying that the rise in flu and the common cold coincided with norovirus, which has forced some hospital wards to close to control infections. Professor Field added: “We are not just seeing flu-like symptoms, but proper influenza, which means people not being able to get out of bed, and which can lead to more serious illness such as bronchitis.

“Along with norovirus, which lasts for 48 hours, and other bugs that cause colds, this is a real congruence of villains.” People suffering from norovirus or colds usually recover in two to three days, but should stay away from doctors’ surgeries and hospitals to avoid spreading it to others, he said.

In hospitals, patients are already facing long waits in ambulances and on trolleys, John Heyworth, president of the College of Emergency Medicine, said. “The system simply does not have enough capacity to cope with the pressure it is under, and we expect this to keep getting worse over Christmas and then over the next three to four weeks,” he said.

Richard Pebody, consultant epidemiologist the HPA’s centre for infections, said: “The best ways to decrease chances of flu is to practice regular hand washing and good respiratory hygiene – covering mouth and nose when coughing or sneezing.”

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