Thanks again for all the input guys, now I'm really undecided - there seems to be as many people saying 'go for it' as there are saying 'don't do it!' LOL
I was a bit worried at the number of people suggesting a potential fire hazard - it wasn't something I'd considered to be honest, I've not only been a PC enthusiast all my life, but I've worked in IT, where I've built and repaired perhaps hundreds of PCs over the last 15 years and have never come across - or heard a report of - a PC which had actually combusted. Many's the time I've seen a PSU blow with a bang and a little puff of smoke, but never with naked flames emitting. I'm not saying it's not possible, but surely (during normal, sensible operation) the risk of this happening is absolutely miniscule - I'm more likely to be hit by a car, right?
It made my concerned about my rig even in its current location - I pretty much leave it turned on all day when I'm at work and have done years - surely the fire-risk is as great in my study when no one is in the house as it is in the loft... ?
Anyway, I appreciate the tip. For the money - peace of mind pay-off: I'll be fitting a smoke alarm.