Well update,

Changed everyone's food to highlife (sp?) and removed biscuits, got a water fountain, kept putting him into his litter when he looked like he was going to spray, cleaned heavily sprayed areas with biological cleaner and deoderiser, and (fingers crossed) we've had no signs of cystitis and no spraying for 2 days.

I do however have another question - Is there any good dried food which won't cause agravation to cystitis?

Thanks All