A doctor has issued a stark warning about a virus poised to tear across the UK with the doctor saying it could be a 'very bad' winter.

Prof Adam Finn, Professor of Paediatrics, University of Bristol, gave an update about the looming flu season, which he said has started earlier than usual.

He said: "This is worrying because it suggests that the strain or strains in circulation are finding it easier than usual to spread about and so are doing so before the colder weather conditions that usually signal and drive the onset of the season.

“An important possible explanation for this could be that there is less immunity than usual in the population controlling the spread of flu viruses."

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The NHS has issued a "flu jab SOS" as fears continue to grow among experts that this will be a brutal winter. The strain he is particularly concerned about is called H3N2, which has developed some worrying mutations.

He said: “When a completely novel strain of flu that can spread between people arrives against which no one has immunity, we call it a pandemic, and very large waves of infection occur at any time of the year.

"But sometimes a new strain develops that isn't entirely new but sufficiently new to enable it to spread more efficiently because our immunity from previous infections and vaccinations is not that well matched."

He continued: “This is what may be happening this year as one of the strains of influenza A that we are familiar with - called H3N2 - seems to have acquired several new mutations over the summer and is responsible for many of the flu cases showing up now.

“The other reason why the early start of this year's flu epidemic is a worry is that there has not been enough time yet for a lot of people to get vaccinated.

"The children's programme kicked off in September and the adult programme in October.

"Usually, November is a month when a lot of people get the vaccine before the infections start to spread in December and January."

Professor Finn added: “Even though this new strain of H3N2 has arrived and it is different from the H3N2 strain in this year's vaccines, they should provide some degree of protection against this strain and certainly against the other flu strains that may be coming through as the winter goes on.

"The bottom line is that it's looking possible that we may be facing a very bad flu season this year and the best thing we can all do right now to tackle the problem is to get vaccinated.”