NHS 111 call handlers service have been left "working on paper" after the failure of IT systems, according to a letter from NHS England to London GPs seen by industry magazine Pulse.

The attack had wide-ranging implications, affecting the system used to dispatch ambulances, book out-of-hours appointments and issue emergency prescriptions and severely affecting response times across all four UK nations. 

The Birmingham-based firm says it first spotted the hack at 07:00 BST on 4 August and immediately took steps to contain the hackers. The Welsh Ambulance Service was one of the firsts to report a "major outage" of the system used to refer patients from 111 to out-of-hours GP providers. 

"We are rebuilding and restoring impacted systems in a separate and secure environment," said a statement published by Advanced. 

The NHS insists that disruption is minimal, but Advanced would not say if NHS data had been stolen or whether the...