The number of people falling ill with flu has dropped to a record low for this time of year.

Official figures show fewer people are turning up at GP surgeries with flu symptoms compared with any other winter since 1967, when statistics were first collected.

Experts at the Public Health Laboratory Service said they are unable to explain why infection rates are so low.

The rates are incredibly low Dr Carol Joseph, PHLS

But they warned that a flu outbreak could still occur.

Doctors said recent cold weather and the re-opening of schools and offices after the Christmas holidays could help the virus to spread.

The PHLS figures show that GPs across the UK have seen very few people with flu-like illness over the past seven days.

GP consultations

Consultations for flu-like illness in England were just 27 per 100,000 of the population in the first week of January. This is up marginally on the previous week but is still remarkably low for this time of year.

There were similar rates in Scotland, Wales and Northern Ireland.

Dr Carol Joseph of the PHLS said infection rates were well below what GPs would normally expect.

"The rates are incredibly low," she told BBC News Online. "It is well below the rates we would normally expect at this time of year which are somewhere between 100 and 200 per 100,000."

Britons are not the only ones who appear to have escaped the virus. Rates of infection are also low across Europe and the United States.

"We don't really know why rates are so low," said Dr Joseph. "This is the third year running we haven't seen very much flu and it is the same in a lot of countries.

"The influenza virus is a law onto itself. It may be lying low before it comes back and hits us hard or it could be losing its virulence. It is an interesting phenomenon but we cannot explain it."

Dr Joseph acknowledged that greater uptake of the flu vaccine in the UK could be one factor.

But she warned members of the public to be on their guard against the virus.

"If anything is going to happen, it is going to happen now," she said.

"The recent cold weather and the re-opening of schools and offices after the Christmas holidays and the greater mixing of people could see means that an outbreak could start happening soon."