The latest official data suggest Scotland is faring the worst, as it is currently the only country in the UK where GP consultation rates have reached ‘medium’ intensity. England, Wales and Northern Ireland all have ‘low’ - but rising - levels.
In England in week 52, the overall weekly influenza-like illness was 21.0 per 100,000 in England, up from 18.9 the week before. It must exceed 26 to be considered medium intensity.
The report warns this data should be interpreted with caution, as GP practices were only open for three days over the week due to bank holidays.
However, looking at hospital admission for flu-like symptoms, the number of new cases admitted rose from 61 in week 51 to almost twice as many at 114 in week 52. Public Health England said on Twitter that hospitalisation rates were 2.5 times the level compared with the same time last year - telling people it was 'not too late' to be vaccinated.
This puts the number of cases firmly in the 'very high' category, and close to twice the number reported in 2016.
At the same time, the total number of confirmed deaths for the season so far more than doubled over this timeframe from 23 to 48.
GPonline reported last month that two thirds of GP practices feared they would be unable to cope with winter pressure - with many warning that even before the impact of seasonal demand, existing heavy workload in primary care had pushed them close to breaking point. GPs warned that they would be in no position to absorb the impact of a major flu outbreak.
The rise in flu cases may stoke fears that the UK is set to experience a heavy flu season, after countries in the southern hemisphere including Australia underwent one of its most deadly on record.
It comes after the number of GP consultations spiked in the week before, with cases rising by two thirds in England.
Winter pressures have already led NHS England to advise that all non-elective operations should be deferred until after January.