On Monday night primary care leaders said the breakdown had “serious” implications for patient care

“Healthcare professionals rely on email to communicate with each other, so it’s essential that we have a secure platform, such as NHS Mail, to do so,” said Professor Maureen Baker, Chair of the Royal College of GPs.

Frontline staff were less measured, however.

One renal surgeon posted on Twitter: “I hope they reserve a special place in hell for those insisting on replying to all.”

Another user, a health service manager, said: “So essentially #NHSmail users have all just carried out a DDoS [distributed denial of service] attack on themselves.”

The current system, formally known as NHS Mail 2, was introduced in May, implemented under a Department of Health contract by the professional services firm Accenture and business technology company Avanade.

It is used across the both the English and Scottish health services, although the problem only affected the 840,000 accounts in England.

“Mistakes happen, of course, but when it means urgent messages about patient care aren’t getting through, or that receiving important information is delayed, it becomes a very serious issue,” said Professor Baker.

“We hope this situation with NHS Mail can be rectified swiftly, and question whether such a situation was foreseen in the risk assessment, and whether mitigating actions, such as safeguards being put in place or guidance issued as to how to properly use the platform, will be taken to avoid this happening again.”