Current UK CompSci PostDoc here - and yeah, pretty much what everyone says here is correct. My contract is 'contingent on funding' (so casual/short-term by any other name, but 'perminant' so HR can fudge their short-term employment numbers down) and my pay is well below what I could get in the wider industry.
I stay because I'd like to think I can improve things (I'm very active in management talks, where I can be) but as we're now at 6 (? Maybe 7) years of below-inflation pay adjustments, and with no progression possible at my grade unless I make the leap to lecturer or equivalent I'm just stuck here and its getting tiresome, and every year I look at my bank and go 'why am I doing this?'.
One day I'll stop asking why and leave, but I like what I do - its just not economical.
... and for the curious, I've made the case for promotion and applied for it a number of times, but as no-one ever retires in the industry (profs forever?) the next grade up is stupidly over-subscribed, so my chances are extremely low.