The attack, which 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, means the affected hospitals cannot currently match patients' blood at the same frequency as usual.

O positive and O negative donors are being asked to urgently book appointments to give blood.

Professor Stephen Powis, medical director for NHS England, said: ‘NHS staff are continuing to go above and beyond to minimise the significant disruption to patients following the ransomware cyber-attack on Synnovis.'

Prof Powis said a number of operations and appointments had been postponed or diverted to neighbouring hospitals as pathology services for the most clinical urgent cases were prioritised.

The Independent reported over 200 emergency and life-saving operations, including those which should be done within 24 hours, had been cancelled by Guy's and St Thomas' Foundation Trust and King's College University Hospital NHS Foundation Trust.