I had the same experience. The hospital had wi-fi, but I as a mere patient wasn't allowed access. No-one would explain why, that's just the way it was.
Maybe there is a valid reason, but it struck me as a classic example of British bureaucratic small-mindedness. I would've thought in these days of virtually unlimited broadband, with things like BT infinity, offering wi-fi to your 'customers' (as they like to call us nowadays) and the poor sods who have to wait around for hours on their account, would be a no-brainer. I'm sure if challenged they'd come up with some twatty nonsense about data protection or something...and when you queried how the mighty minds at the NHS can't grapple with something that Costa, the London tube network and every arse-end pub and cafe in London seems to be able to handle, they'd give you that famous pursed-lip 'just ate a lemon' look and say "that's the hospital's policy".