Re: Cost is the smaller concern
"What? PCs already come with a Windows license."
Its the other software that MS makes money from. It's long been the case that MS could afford to give Windows away (which is why they tolerated piracy for so long) as long as they could sell copies of MS Office.
As others have already observed the vast majority of PCs in the NHS are doing basic functions (web browsing and word processing). As such they could be replaced with lightweight clients.