Most patients saw no change to hospital services on Monday and all local doctors' surgeries opened after a cyber attack hit dozens of computers in Britain's health service, interior minister Amber Rudd said.

"The vast majority of patients have noticed no difference," Rudd told BBC television, describing the work of Britain's National Health Service over the weekend as "heroic".

"The reason why so many patients have been unaffected today is because they were ready for this, they had staff who came in over the weekend to make sure patients were unaffected," she said.

Only two health trusts were still "impacted" by the attack on Monday, far fewer than the 47 on Friday, Rudd said.