A planned strike by Britain’s National Health Service (NHS), as part of a broader work stoppage by public sector workers over pension reforms, could lead to a 20 percent drop in health care capacity, warned government officials.

The Department of Health said it fears that one-in-five health care workers could walk off the job on November 30, leading to the cancellation or postponement of 5,500 pre-planned operations and 12,000 diagnostic tests.

Reportedly, another 40,000 outpatient appointments would be delayed.

Andrew Lansley, the Secretary of State for Health, has urged NHS staff-members to reconsider their decision to strike.

I would ask staff, despite what their trade union says, to consider carefully whether going on strike is the right thing to do,” he said.

We have to put patients first. The NHS and those working in the health service should never take action that would prejudice the interests of patients. It is especially irresponsible to do so when there continue to be active discussions with the trade unions.

Similarly, a spokesman for the Department of Health warned: Many outpatient clinics and non-urgent operations will have to be cancelled. Essential treatment such as dialysis or chemotherapy will be prioritized as well as urgent cases that crop up on the day.

In response, the Unite union, which represents the imminently striking workers, dismissed the government’s warnings as scaremongering.

Rachael Maskell, who is the chief health care worker representative at Unite, said: I don't recognize these [government] figures at all. It's irresponsible to scare the public in this way. We have been very clear about the date of industrial action for a long time. We would have to question why trusts are even booking operations for November 30.

She added: Our members are saying enough is enough -- and that they intend to exercise their legal and democratic right to take industrial action to defend their pensions.”

Unions have promised that the strike will not compromise patient safety, and claim they have made arrangements such that hospitals will operate on public holiday levels of service.

Different trusts will be affected to different degrees, depending on their level of union membership, said Dean Royles, director of NHS Employers.

On Thursday, Danny Alexander, chief secretary to the Treasury, warned of the “significant” impact on the economy that an NHS strike would have.

“We estimate in the worst case scenario potentially half a billion pounds of lost output to the United Kingdom,’ he said at a London press conference.

The Treasury has said that if all of the 900,000 public sector workers who voted to strike actually do, the output by state employees would drop by 15 percent.