There are three books with contain between them most of what you need to know. The first is the regulations themselves BS7671:2008 and even after years in the trade I still need to refer to the main book for any non run of the mill work. Guidance notes 3 is the other book which is the main book explaining how to inspect and test and the last is guide to the 17th Edition which gives guidance as to how many cables can be fed through conduit etc. This latter book help to integrate the electrical system into the other regulations as well. As to down loadable there is of course Part P and the other parts of the building regulations like M and L which also affect the electrical systems.
In theory you could learn from the books but in practice there are items which do need more hands on like SWA glands etc. and just knowing the gland for flame proof is different even if you never use one. And normally only electricians with experience will do inspecting and testing. Remember the paper work may still be valid 10 years after the event and may have copies held by county council building control and if there is cause could be requested by the courts so a mistake may result in a court appearance well after you have any memory of the events.
I know I have made mistakes which have been lucky for me pointed out by lectures and not after an accident but one wonders if one does not know how to get the information if you really have the experience required?
We will of course try to help with any questions but I would expect an experienced electrician to need around a weeks tuition i.e. 30 hours before taking the C&G 2391 exam.