Look mate, sorry to burst your bubble but 99% of DIY sparkies ain't got a scoobie what they're doing. Its as simple as that. Sure they may be able to follow a nice wiring diagram but they won't have a clue when it comes to testing, safe zones for a bathroom, cable calcs etc etc. So whilst you may be able to convince your missus that you are saving a few quid - you are mugging yourself off at the same time. If DIY electrics was such an easy thing then it wouldn't be banned in most countries. However enjoy your DIY electrics whilst you can, because it will be banned here soon as well. Part P - Do you know what this is by the way? Is the first step to stopping Mr DIYer.
Sorry mate, but amateur electrics kill.