In England, 13.1% of GP consultations per 100,000 registered patients were for flu-like illness in week 49 of 2019 - just above the baseline threshold of 12.7 for a low-level epidemic.
Cases increased from 10.6 per 100,000 registered patients in week 48 - and are now at more than double the level seen in week 47.
In parts of England and the UK as a whole, however, cases have surged faster - reaching medium to high levels.
In the north of England NHS region, cases hit 25.4 per 100,000 registered patients in week 49 - double the baseline threshold. Cases are also high in the Midlands and east of England region - at 14.1 per 100,000 patients, but remain below the baseline threshold in London and the south of England.
Cases are highest among the under-15 age group, with 18.5 cases per 100,000 patients in England.
In Northern Ireland, flu cases have spiked even more sharply - rising to 29.2 per 100,000 patients - double the baseline threshold of 14.7 for the country - while in Wales and Scotland flu remains below the baseline.
Hospital data for England, meanwhile, show that there were 472 hospitalised confirmed influenza cases in week 49 - a figure that has risen sharply over recent weeks and continues to climb.
The rise in flu cases comes just a month after the BMA warned that the NHS was heading for its worst winter ever because of high pressure throughout the health service that continued throughout summer this year.
Data published this week show that numbers of patients waiting on trolleys in NHS hospitals are at their highest level ever and that not a single major A&E department in England met the current four-hour waiting time target.