The potent flu strain threatens to exacerbate the NHS’ winter crisis with one in four hospital flu admissions now down to the H3N2 bug.

In the last week of December, 112 people were admitted to hospital with Australian flu alone, out of 421 cases. 17 of those were admitted to intensive care units.

And according to Public Health England (PHE), the rate of flu hospitalisation tripled from 2.33 cases to 6.82 cases per 100,000 people at the same time.

Since October 2, 355 people have been admitted to intensive care with flu - 45 of those with the Australian strain.

There have been 48 flu deaths in the UK over the same period.

The annual winter crisis in the NHS deepened this week as the flu jab was revealed to be ineffective.

PHE warned of a flu outbreak as the vaccine most commonly given out by the NHS targeted the wrong strain of the virus.

At-risk people, such as the elderly, who were vaccinated against influenza could still get the flu as the NHS jab is not effective against the most common flu strain being picked up.

‘Trivalent’ flu vaccines given out by the NHS don’t cover an influenza B strain that has already been spotted in 21 out of 25 PHE lab tests.

Patients who had a ‘quadrivalent’ vaccine instead will be covered against the strain - but this jab is more expensive and thus less common for NHS patients.

In the last week of December, the rate of GP consultancies for flu-like symptoms was nearly double the expected baseline rate - though PHE says bank holidays may account for some of this.

It comes as at least 24 NHS trust went into “black alert” emergency measures having run out of staff or space.

Just two trusts had issued this kind of warning at this time last year. The figure is likely to be an underestimate as many trusts refused to say whether they had taken emergency measures, and the information is not publicly available.

Bedford Hospital NHS trust begged families to collect their elderly relatives from hospital and look after them at home as bed occupancy hit 100 percent.

The trust said: “Many of our patients are elderly and require support after discharge, and we ask that relatives support us and their loved ones by helping us discharge patients that are medically well to leave hospital; to return to the most appropriate environment such as their own home or a community care home.”

Meanwhile, NHS England’s national emergency pressures panel has recommended pausing non-urgent operations until the end of January and postponing routine appointments amid increased winter demand.