"Some expensive hardware (such as MRI scanners) cannot be updated immediately, and in such instances organizations will take steps to mitigate any risk, such as by isolating the device from the main network,"
This sounds like misdirection. With 4.7% of NHS computers running XP, are they really suggesting that something approaching one computer in twenty has some fancy diagnostic equipment which is at least 8 years old attached to it? This must be a tiny proportion of the XP computers in the NHS. What about the rest?