The virulent disease could prove as deadly as Hong Kong flu in 1968 which killed a million people worldwide, experts warned yesterday. 

The elderly are feared to be most at risk because vaccines are not providing enough protection. 

Last night just five areas of the country were free from all strains of the disease – including the feared H3N2 Aussie strain. 

The number of people being treated in hospital for flu tripled over the Christmas week.  

Now it is feared NHS chiefs may be forced to cancel more operations and appointments to cope with a surge of patients in the coming weeks. 

Hospital bosses have so far been forced to delay around 55,000 procedures. 

Professor Robert Dingwall, from Nottingham Trent University, told the Daily Express yesterday: “The problem with the new Aussie flu is that the vaccine is not as good as it is for the other strains because it is a new strain.

“By the time the Aussie strain had been identified, this year’s vaccine had already been manufactured.  

“We are looking at a flu season that is likely to be worse than last year. 

“It is a bit too early to say it could be the worst flu season in a generation. 

“But it could be if the Aussie strain really takes hold. 

“Flu is very infectious and once it gets into the country, there’s nothing much you can do about it. 

“It might mean the system remains at this intensity for another four to five weeks instead of returning to normal as we would expect.  

“That could mean elective surgery has to be cancelled well into February.” 

Public Health England data shows flu-related hospital admissions tripled from 2.33 per 100,000 people to 6.82 between Christmas Eve and New Years Eve. 

This suggests the number of flu patients in hospital soared from 1,280 to 3,750 in just one week, with 17 said to be in intensive care. 

Fears of fatalities have been growing after the lethal virus claimed its first victims in Ireland. 

In France at least 30 people have died and 11,500 treated in hospital.  

Areas worst hit in the UK include Portsmouth, Plymouth, Dundee, Doncaster, Chelmsford, Northampton and Canterbury. 

But Dorset, Ilford, the City of London and two smaller areas have reported zero cases. 

Professor Helen Stokes-Lampard, chairwoman of the Royal College of GPs, said: “Whilst this is currently within seasonally-expected levels, we are also hearing anecdotal reports of increased demand at surgeries. 

“We want to reassure patients that the influenza vaccine remains the best protection. 

“It is not too late for patients to receive their vaccination.”  

Aussie flu symptoms include a sore throat and cough, headache, fever, muscle ache, fatigue and sneezing. 

But some patients have told how they been sick and suffered hallucinations. 

With growing concern over delays in emergency treatment, Theresa May was yesterday forced to defend the Government’s record on the NHS, insisting it had “put the money in that was asked for”. 

But she told the BBC’s Andrew Marr Show: “Of course nothing’s perfect and there is more for us to do.”  

The admission came after Mr Marr, who survived a stroke in 2013, told her he would have died if he didn’t receive urgent care. 

He highlighted how a woman waited more than five hours to be admitted to Broomfield Hospital in Chelmsford, Essex. 

He added: “If I’d been waiting for five hours before I’d seen a doctor after my stroke, I would not be here talking to you.

“This is about life and death and up and down the country people are having horrendous experiences of the NHS.”