NHS organisations across the country are braced for significant disruption as nurses prepare to stage a 28-hour strike over pay.

The Royal College of Nursing (RCN) will hold industrial action from 8pm on Sunday until 11.59pm on Monday night after voting to reject the latest Government offer.

The union initially said it would not agree to derogations – broad areas of care where staffing is guaranteed despite industrial action – but granted some exemptions on Friday in an apparent U-turn.

Great Ormond Street Hospital (GOSH) is among organisations where nurses have agreed to derogations after it voiced “serious concerns” about patient safety during the walkout.

The hospital said it was “incredibly grateful” to RCN members for offering assurances but took the decision not to stand down a “business continuity incident” it had previously declared until it was confident it could staff its services over the strike.

Health workers across the NHS have gone on strike several times in past months in disputes over pay and conditions.

Unions including Unison and the GMB have voted in favour of a Government pay offer to end the strikes, while Unite and the RCN have voted against.

RCN general secretary Pat Cullen defended the strike and said cancelled medical appointments were not just the result of industrial action.

NHS England is urging the public to use the health service wisely.

It said emergency and urgent care would remain the priority, with people asked to use other services such as pharmacies and 111 where possible.

Nurses make up a quarter of NHS staff and are the biggest proportion of the health service workforce.

NHS England warned that staffing levels for some areas of the country will be “exceptionally low, lower than on previous strike days”.

It added the number of rescheduled appointments due to strike action is set to hit half a million next week.

A High Court judge ruled on Thursday it would be unlawful for the RCN strike to continue into Tuesday as originally planned, meaning it will now end just before midnight on Monday.