Friday's attack was the latest in the growing menace of ransomware in which hackers deliver files to computers that automatically encrypt their data, making it unusable until a ransom is paid.
The U.K.'s National Cyber Security Centre said new cases of so-called ransomware are possible "at a significant scale".
Security experts have warned that another attack is imminent, most likely on Monday, and could be unstoppable.
"Patients are no longer being diverted away from hospital accident and emergency units", Anne Rainsberry, NHS England's national incident director, said in a statement.
"There was an impact on appointments and the general operation of the surgeries but they were still open".
"Our priority has been to restore our radiology services, and like other trusts affected working with NHS Digital, we will continue to do all we can to protect our systems for the future". In December it was reported that nearly all NHS trusts were using an obsolete version of Windows that Microsoft had stopped providing security updates for in April 2014.
Technology powerhouse Microsoft have also responded by re-releasing security updates for older versions of their Windows software in order to mitigate further outbreaks.
But it added that GP practices across the region are "still asking patients to consider delaying contacting their practice unless they really need to for the next few days to allow time to clear backlogs caused by the cyber-attack".
Several hospitals were still facing disruptions on Monday, with St Bartholomew's in London cancelling appointments and warning of delays to pathology and diagnostic services.
"The reason why so many patients have been unaffected today is because they were ready for this", she said.
Mikko Hypponen, chief research officer at the Helsinki-based cyber security company F-Secure, told AFP that the attack was "the biggest ransomware outbreak in history", saying that 130,000 systems in more than 100 countries had been affected.
An NHS update for the North East and North Cumbria said its primary care computer network was switched back on yesterday afternoon, with practices back up and running this morning.