The attack took place on Monday, 3 June on Synnovis IT systems at Guy's and St Thomas' NHS Foundation Trust, and King's College Hospital NHS Foundation Trust.

A spokesperson for NHS England London region said the attack was having ‘a significant impact on the delivery of services at Guy's and St Thomas', King's College Hospital NHS Foundation Trusts and primary care services in south east London'.

NHS England said some patient care had been cancelled or redirected to other providers as urgent work was prioritised.

Mark Dollar, Synnovis chief executive, said the attack had interrupted many pathology services, adding: ‘This is a harsh reminder that this sort of attack can happen to anyone at any time and that, dispiritingly, the individuals behind it have no scruples about who their actions might affect.'

Synnovis said the incident had been reported to law enforcement and the Information Commissioner, adding it was working with the National Cyber Security Centre and the Cyber Operations Team.

The incident came after a ransomware group published stolen patient data stolen from NHS Dumfries and Galloway in March following a cyber attack in February.