And there's so much more to it than just the end user
Well said Sir!
There's so much more to running an IT infrastructure than simply the cost of the software. In fact I would guess the NHS has done the Math (well being the NHS this may not be true) and decided that as an overall part of it's IT budget paying for Software or getting it free - doesn't make much difference.
It's not just retraining the end user in using Libre Office. What do you do with all the trained up MS network admins who then have to retrain to use Linux. It costs thousands (millions even) for the NHS just to keep these guys trained up in MS tech. They need their costly certificates as you can't let an uncertified admin anywhere near a network with patient information on it.
Then there are the 3rd party suppliers. It's not for no reason that the NHS is still stuck on IE6. All those extra Active-X plugins JUST WORK. Move to any other browser (even IE9) and they need to be retested.
Then there is the web infrastructure which in the NHS almost exclusively uses .Net and Sharepoint and so on.
The list goes on and on.
And don't for a second think that an organisation the size of the NHS, with the purchasing price is paying anywhere near the published price of the software. I would expect discounts of over 50%.
In fact the only crime the NHS is performing is that they are paying for MS software at all. MS make so much money out of 3rd party suppliers to the NHS that the NHS should be getting their software for free!