NHS patients have been warned to expect delays and postponed operations tomorrow during the country’s biggest strike for a generation.

However, doctors say A&E services will be maintained and that seriously ill patients will not be abandoned.

Hundreds of North-East nurses, healthcare assistants, paramedics, physiotherapists, and support staff such as cleaners and administrators, will join the action against changes to public sector pensions.

County Durham and Darlington NHS Foundation Trust, which runs hospitals in Durham City, Darlington and Bishop Auckland, said managers had worked closely with the unions to ensure that emergency services did not face disruption.

A spokesman said: “Some planned services are running at 75 per cent of normal capacity, but anyone who has an outpatient appointment or is coming in for surgery on Wednesday should do so as planned. All acute and emergency services, such as A&E, will be running.”

South Tees Hospitals NHS Foundation Trust, which runs the Friarage Hospital, in Northallerton, North Yorkshire, and The James Cook University Hospital, in Middlesbrough, said it hoped to run a full range of emergency and essential services.

Patients have already been contacted where operations or clinics have been postponed.

North Tees and Hartlepool NHS Foundation Trust said 39 planned operations would be postponed. They were nonurgent and not related to cancer.

The North-East Ambulance Service said it expected to operate a near-normal 999 service and high-dependency transport service.

However, urgent but non emergency calls, where a request for transport has been made by a doctor or GP, would face significant delays.

Transport to appointments at clinics and hospitals would be limited only to people needing dialysis, cancer care or other serious illness treatment.