I woke up at 6.30 this morning so I could be outside B&Q first thing so I could fix up the cistern and turn the water back on. Despite its super store status it didn't have any ball cock valves with shorter arms. Instead I went for a compact armless mechanism which works quite well. Unfortunately it turned out the mechanism gets in the way of the syphon mechanism (the bit that actually flushes the cistern). I've temporarily worked around the problem by reversing the orientation of the syphon but this means you have to flush the loo by manually pulling the syphon hook. I'm trying to work out if the best solution is to jury rig the flush handle with a coat hanger or replace the syphon with a more modern mechanism. I just wish the screwfix site had the dimensions of these things.
There is a positive side to all of this though. As I do more and more DIY I'm getting more confident with taking stuff apart and putting it back together. Not quite ready for boiler fitting just yet though ;-)