In the week ending 5 January, GP consultations for flu-like illness in England increased by 113 per cent to 38.2 per 100,000.
A study of samples from 488 GP surgeries around the UK showed the outbreak is caused by an influenza B strain.
Dr Douglas Fleming, Birmingham GP and member of the Joint Committee on Vaccination and Immunisation's influenza subcommittee, said GPs should follow NICE guidelines on antiviral use, despite suggestions the drugs should be reserved for use during an epidemic or pandemic.
In England and Wales, the increase in flu consultations has been particularly great in the five to 14 age group.
'This is because the main strain circulating is influenza B,' said Dr Fleming.
NICE recommends that oseltamivir (Tamiflu) is prescribed to at-risk individuals over 13 years not protected by vaccination and who have been exposed to flu-like illness. Zanamivir (Relenza) is recommended for treatment of patients over 12 years.