Re: How about...
"What is the NHS getting out of it, not what benefit is there for the patients."
Depends what the data is used for, but from a research point of view, having the medical records of every person in an entire country from birth to death could bring all kinds of benefits.
For example, you could cross reference the first few digits of a patients contact number with cancer rates, thereby showing if people who use a mobile phone (ie their contact details start with an 07 number) are getting brain cancer. Don't forget, this data goes back decades and covers millions of people, so you could draw some pretty solid conclusions.
I agree that this particular suggestion (especially the voluntary nature of these guidelines) is pretty iffy, but there is definitely benefits to allowing some researchers limited access to NHS data (with strong oversight).