You've brightened up my day a bit, thanks

.
Knowing my luck, even getting near to removing the cylinder head would lead to all sorts of problems with the head gasket, exhaust etc. etc. so it's well worth leaving it where it is. The fact that I recently changed the timing belt and will have to disturb it, is annoying enough.
I assume that you still need a tool to compress the valve springs. There's something that looks good for the job in the Machine Mart (18 quid) catalogue next to a compressed air adaptor (11 quid) which you would need to use the method VR6 suggested.
I am wondering, if this sort of job would cost upwards of 300 quid to get done by someone more capable with a spanner than me, then I could just about convince my girlfriend that the cost of a compressor (200 quid) is justified

. I do not think that is possible to have too many tools.