Pat Cullen, chief executive of the Royal College Nursing (RCN), says the union is already looking at potential strike dates next month if it fails reach a pay deal with the Government for its members.
Nurses have braved -8C temperatures to walk out at hospitals across the UK, where only a Christmas Day service is being provided amid a row over pay and conditions.
Dame Ruth May, Britain s most senior nurse, joined strikers at a London hospital, as she urged ministers seek an urgent resolution with the union orchestrating the action.