Fears are growing that Monday could see a surge in the number of computers taken over by the devastating WannaCry ransomware hack.

As people return to work and connect laptops to their office system, this could potentially spark a new wave of infections.

About 200,000 victims in 150 countries or more have so far been affected, although this number was reduced after a 22-year-old British security analyst accidentally triggered a hidden ‘kill switch’.

But the analyst, known as MalwareTech on Twitter, warned the hackers could easily reconfigure the software to get around this and urged people to instal a patch issued by Microsoft.

Some 48 out of 248 NHS trusts in the UK were affected although this was reduced to just six trusts within 24 hours of the start of the attack.

Marin Ivezic, a Hong Kong-based cybersecurity partner at financial giant PwC, told Reuters that some clients had been "working around the clock since the story broke" to restore their computer systems.

Some clients were abandoning their usual cautious testing of patches "to do unscheduled downtime and urgent patching, which is causing some inconvenience”, he added.

And Rob Wainwright, head of the European Union police agency, Europol, warned anyone who thought the problem was going away was mistaken.

"At the moment, we are in the face of an escalating threat. The numbers are going up, I am worried about how the numbers will continue to grow when people go to work and turn (on) their machines on Monday morning,” he said.

Christian Karam, a Singapore-based security researcher, underlined this point.

"Expect to hear a lot more about this tomorrow [Monday] morning when users are back in their offices and might fall for phishing emails" or other scams, he said.

One analyst suggested he had already seen WannaCry ransomware 'worms' without the kill switch in circulation, but he later backtracked saying this was not actually the case, adding "my bad".

However the hackers are widely expected to try again.

Darien Huss, a research engineer who assisted the anonymous 22-year-old British researcher who has been lauded a hero, said he was "still worried for what's to come in the next few days, because it really would not be so difficult for the actors behind this to re-release their code without a kill switch or with a better kill switch".

"Or we could potentially see copycats mimic the delivery or exploit method they used," he said.

There are concerns that patient safety may have been compromised by doctors and other medical staff being unable to access medical files.

Dr Mark Porter, who chairs the British Medical Association’s council, said: “This cyber-attack on NHS information systems is extremely worrying for patients and the doctors treating them.

Everyone the Government blames for the NHS crisis – except themselves Show all 6 1 /6 Everyone the Government blames for the NHS crisis – except themselves Everyone the Government blames for the NHS crisis – except themselves The elderly “We acknowledge that there are pressures on the health service, there are always extra pressures on the NHS in the winter, but we have the added pressures of the ageing population and the growing complex needs of the population,” Theresa May has said. Waits of over 12 hours in A&E among elderly people have more than doubled in two years, according to figures from NHS Digital. Getty Everyone the Government blames for the NHS crisis – except themselves Patients going to A&E instead of seeing their GPs Jeremy Hunt has called for a “honest discussion with the public about the purpose of A&E departments”, saying that around a third of A&E patients were in hospital unnecessarily. Mr Hunt told Radio 4’s Today programme the NHS now had more doctors, nurses and funding than ever, but explained what he called “very serious problems at some hospitals” by suggesting pressures were increasing in part because people are going to A&Es when they should not. He urged patients to visit their GP for non-emergency illnesses, outlined plans to release time for family doctors to support urgent care work, and said the NHS will soon be able to deliver seven-day access to a GP from 8am to 8pm. But doctors struggling amid a GP recruitment crisis said Mr Hunt’s plans were unrealistic and demanded the Government commit to investing in all areas of the overstretched health service. Getty Everyone the Government blames for the NHS crisis – except themselves Simon Stevens, head of NHS England Reports that “key members” of Ms May’s team used internal meetings to accuse Simon Stevens, head of NHS England, of being unenthusiastic and unresponsive have been rejected by Downing Street. Mr Stevens had allegedly rejected claims made by Ms May that the NHS had been given more funding than required. Getty Everyone the Government blames for the NHS crisis – except themselves Previous health policy, not funding In an interview with Sky News’s Sophy Ridge, Ms May acknowledged the NHS faced pressures but said it was a problem that had been “ducked by government over the years”. She refuted the claim that hospitals were tackling a “humanitarian crisis” and said health funding was at record levels. “We asked the NHS a while back to set out what it needed over the next five years in terms of its plan for the future and the funding that it would need,” said the Prime Minister. “They did that, we gave them that funding, in fact we gave them more funding than they required… Funding is now at record levels for the NHS, more money has been going in.” But doctors accused Ms May of being “in denial” about how the lack of additional funding provided for health and social care were behind a spiralling crisis in NHS hospitals. Getty Images Everyone the Government blames for the NHS crisis – except themselves Target to treat all A&E patients within four hours Mr Hunt was accused of watering down the flagship target to treat all A&E patients within four hours. The Health Secretary told MPs the promise – introduced by Tony Blair’s government in 2000 – should only be for “those who actually need it”. Amid jeers in the Commons, Mr Hunt said only four other countries pledged to treat all patients within a similar timeframe and all had “less stringent” rules. But Ms May has now said the Government will stand by the four-hour target for A&E, which says 95 per cent of patients must be dealt with within that time frame. Getty Images Everyone the Government blames for the NHS crisis – except themselves No one Mr Hunt was accused of “hiding” from the public eye following news of the Red Cross’s comments and didn’t make an official statement for two days. He was also filmed refusing to answer questions from journalists who pursued him down the street yesterday to ask whether he planned to scrap the four-hour A&E waiting time target. Sky News reporter Beth Rigby pressed the Health Secretary on his position on the matter, saying “the public will want to know, Mr Hunt”. “Sorry Beth, I’ve answered questions about this already,” replied Mr Hunt. “But you didn’t answer questions on this. You said it was over-interpreted in the House of Commons and you didn’t want to water it down. Is that what you’re saying?” said Ms Rigby. “It’s very difficult, because how are we going to explain to the public what your intention is, when you change your position and then won’t answer the question, Mr Hunt”. But the Health Secretary maintained his silence until he reached his car and got in. Getty

“There have been reports of hospital doctors and GPs unable to access patients’ medical records, appointment booking systems and in some cases having to resort to pen and paper.

“NHS staff are working extremely hard to provide the best possible patient care, and we hope NHS Digital are able to resolve these problems as soon as possible.”

He also questioned whether the Government had spent enough on security systems to protect the NHS.

“We need to quickly establish what went wrong to prevent this happening again and questions must also asked about whether inadequate investment in NHS information systems has left it vulnerable to such an attack.”