People including the elderly have been urged to have the flu vaccination and take precautions against illness amid concerns that 'Aussie flu' could hit Britain as badly as it did Australia.
Public Health England (PHE) figures show cases of influenza have risen by 48 per cent in the past week, significantly higher than in previous winters.
In Australia, the H3N2 virus caused 2.5 times the number of flu cases than is normal, resulting in 'standing room only' in hospitals and health care centres, and it has now been confirmed as having reached the UK.
Last week, there were 684 cases of influenza A and 915 of influenza B recorded in England and Wales, with these numbers expected to increase further as 2018 progresses. Britain's flu season typically mirrors that seen in Australia.
Health officials have also said that flu is 'actively circulating' in Ireland, with around ten people having lost their lives to the illness so far.
Studies have suggested that the H3N2 strain that is used in vaccines by the World Health Organisation may have mutated to evade detection, which has been put forward as a reason why the flu outbreak was so severe in Australia and why Britain may now be facing an outbreak.
A spokesperson for PHE said: "The current flu vaccine is still the best defence we have against the virus. We therefore encourage all those who are eligible to take up the offer of the vaccine."
The injection is currently available at pharmacies for a small fee, as well as at doctors' surgeries for the elderly, young children and those with pre-existing health conditions.
PHE also offered advice on avoiding the spread of flu, including sneezing in tissues and then binning them, washing hands regularly and cleaning infected surfaces like computer keyboards.
It recommended avoiding contact with other people if patients are presenting with flu symptoms too, including going to GP waiting rooms.
Flu typically comes on much faster than the common cold, often in a matter of hours, and it symptoms are more severe. However, it should still be treated at home, something many Britons still fail to realise.