Patients are being urged to stay away from GPs amid fears of a “Monday morning meltdown” as a result of the global cyber attacks.

It comes amid warnings that the crisis could spread to other sectors, with a wider “escalating threat” as millions of workers switch on their computers.

The director of Europol raised fears that the cyber attack that has hit NHS services and global businesses “will continue to grow" as people return to work after the weekend.

The head of Britain’s National Cyber Security Centre echoed the warning, raising concerns that many existing infections may yet to have been detected, and others could spread within networks.

He said the crisis could develop “at a significant scale” in coming days.

The leader of Britain’s family doctors urged patients without appointments to stay away from GP practices at the start of the week unless their need is urgent.

Dr Helen Stokes-Lampard, chairman of the Royal College of GPs, said the attacks, combined with precautionary measures, have had an “extensive impact” on GP practices, some of which are likely to struggle on Monday.

Last night, she said: “The concern is that on Monday morning the appointment system may not be working, some places may not be able to access routine results, even the phone lines in some cases may not be working.”