A critical incident has been declared at several major London hospitals due to a cyber attack that has impacted their services.

King’s College Hospital, Guy’s and St Thomas’ - including the Royal Brompton and the Evelina London Children’s Hospital - and primary care services are among those affected.

The cyber attack has affected hospitals partnered with Synnovis, which is a provider of pathology services.

It has led to the cancellation of operations and the loss of blood transfusions.

Memos sent to the hospitals said the “critical incident” has had a “major impact” on the delivery of services.

Some procedures and operations have been cancelled or have been redirected to other NHS providers as hospital bosses continue to establish what work can be carried out safely.

When did this cyber attack happen?

As reported by BBC News, the incident is thought to have occurred on Monday, meaning some departments could not connect to a main server.

According to the Health Service Journal (HSJ), several senior sources have told it the system has been the victim of a ransomware attack.

One said gaining access to pathology results could take “weeks, not days”.

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Vanessa Welham from Streatham, south west London, said that her husband’s blood test at Gracefield Gardens health centre was cancelled on Monday evening (June 3) and he was informed that local centres were not taking bookings for an “indefinite period of time”.

She told the PA News Agency: “My husband received a text message last night advising his appointment this morning had been cancelled due to circumstances beyond their control, and that all major south London hospitals – King’s, St Thomas’, Guys, Evalina and Gracefield Gardens – are unable to take any bookings for an indefinite period of time.

“He went on to the Swift website and made a new appointment – the earliest available was June 17, but that’s probably questionable.”