LONDON (Reuters) - Britain’s Prime Minister Theresa May apologized on Thursday to tens of thousands of patients whose operations were canceled to free up staff and beds to deal with emergency patients.

FILE PHOTO: Britain's Prime Minister Theresa May visits Frimley Park Hospital near Camberley, Britain, January 4, 2018. REUTERS/Toby Melville

Earlier this week, officials at the National Health Service (NHS) in England recommended that hospitals cancel all non-urgent appointments and operations until next month.

May, during a visit to a hospital outside London, said she recognized it is frustrating for patients who had their operations postponed.

“I know it is difficult, I know it is frustrating, I know it is disappointing for people and I apologize,” she told Sky News.

A flu outbreak, colder weather and high levels of respiratory illnesses have put hospitals in England under strain with many operating at or near full capacity.

The issue is potentially damaging for May, already weakened after losing a parliamentary majority in last year’s election and struggling to pacify her deeply divided party as she navigates the final year of Brexit negotiations.

The NHS, which delivers free care for all and accounts for a third of government spending on public services, is typically one of the most important issues for voters during elections and one which is often regarded as a weakness for May’s Conservative party.

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Opposition parties regularly accuse the government of failing to adequately fund the health service.

“Ministers refused to provide the funding top NHS officials said was necessary and now patients are paying the price,” said Vince Cable, leader of the Liberal Democrats.

Founded in 1948 by the opposition Labour Party, the NHS is a source of huge pride for many Britons who are able to access free care from cradle to grave.

But tight budgets, an aging population and increasingly complex medical needs have left many hospitals struggling during the winter in recent years.

The pressure continues to grow, according to new data on Thursday.

The number of patients stuck in ambulances for at least an hour almost doubled to more 4,700 cases during the Christmas week compared with the week before.

Department of Health guidelines say ambulance crews should be able to hand patients over to hospital staff within 15 minutes of arrival at hospital.

The average bed occupancy for the Christmas week was 91.7 percent. Doctors say that anything above 85 percent is unsafe.

The conditions have led some doctors taking to Twitter to vent their frustrations.

One London-based doctor wrote that conditions were so bad that he was practicing “battlefield medicine”, while another apologized for the “3rd world conditions” caused by overcrowding.