I'm competent enough imo and have all the tools required to do the job.
The tools required would include:-
RCD test meter
Low ohm meter using at least 200ma i.e. not a multimeter
High ohm meter using at least 500 volt again not a multimeter
Loop impedance meter
Prospective short circuit current meter
These are normally combined into three units cost around £750.
You should also have a voltage tester and proving unit although in most cases there is no isolator so it would require the supplier to draw the fuse. See issue 16 Spring 2010 of SwitchedOn.
Depending on a few factors but with a TT system you may also need an earth rod tester so looking at £1000 to buy test kit. OK you may have all this gear but I suspect you didn't know you needed it.
The TT system does need items before and including the first RCD to be double insulated type. I can see point in up to a 300ma S type RCD feeding a array of RCBO's but the more common way would be two 30ma RCD's.
The LABC charges of £100+ mean it is hardly worth DIY'ing this type of work unless part of a larger project and already covered in the LABC charge.
There are four grades of people as far as electrical work is concerned.
Highest is Competent
Next is Skilled
Then Instructed
and finally Ordinary person.
They are not defined as having passed any exam but in the main the insurance companies will require a C&G2391 or 2392 to be considered competent for the work you are doing. As you must understand the dangers in using instruments like the loop impedance meter and insulation tester which if used incorrectly can raise earthed items to 230 or 500 volt above true ground.
I have not seen how the LABC work with Instructed persons as I am competent. But since they are responsible for safety they may well require the supply to be disconnected then they will allow you to do work and then all tested before the supply is re-connected. This could mean days not hours without power. It would also mean calculations as direct reading loop impedance meters need power to work.
You may have all the skills required. But if so, why ask the questions?