Deke,
It's just BS7671.
Depending on he denomination the Church "governing body" may have additional requirements.
They are easy to get hold of, I have most of them.
I've done a few Churches even at my prices because, they have realised the value in getting it right.
Also, after I did one, and they had an insurance/governing body inspection, they were told that it was the first building that the inspector had seen that the electrical systems had documentation that seemed to be correct.
They then felt justified in what they had spent.
Talk to them, explain that you'll do it correctly, and even perhaps offer to throw in the stupid fixes, blanks, labels, reverse polarity, loose connections (undamaged by heat) in as "freebies" as you do the I&T.
Remember also it's I&T not initial verification.
You are legitimately allowed to sample, and if the quote doesn't cover 100% but 100% is needed on a circuit FI it.
Many these days are not as fussy with MI cable etc. I know a couple that are done in pvc/pvc.
Just be realistic, 5 boards is man hours including sub mains.
How many circuits.
Can you sample.
Do you, need, to strip the high level lighting.
Remember GN3 says:
The purpose of periodic inspection and testing is to provide an engineering view on whether or not the installation is in a satisfactory condition where it can continue to be used safely.
A detailed visual examination of the installation is required, together with appropriate tests. The tests are mainly to confirm that the disconnection times stated in Chapter 41 are met.
...
There is no specific requirement to test the installation on every inspection. Where testing requires dismantling, the inspector should consider whether the risks associated with dismantling and reassembling are justified. Dismantling, and particularly disconnection of cables or components, introduces a risk of unsatisfactory reassembly.
...
The requirement of BS 7671 for periodic inspection and testing is for a detailed inspection comprising an examination of the installation without dismantling, or with partial dismantling as required, together with the tests of Chapter 64 considered appropriate by the person carrying out the inspection and testing. The scope of the periodic inspection and testing must be decided by a suitably skilled person, competent in such inspection and testing work, taking into account the information and guidance contained in this section.
(651.2)
I would be charging a man hour per circuit, (submain & board 1 hour), plus some time to do the certification, and probably not dismantling the high level lighting, I would be R2'ing it with a pole if it's class 1, if it's class 2, then possibly not touching it.
This would depend on the previous records, and what they look like, if, they exist.
If the precious records are rubbish, then I would be pushing for a 100% intrusive I&T of every point, and mapping out cable runs etc.
Remember, you are the duty holder when you are there.
Also, whilst this is a Church, you need to remember that EAWR still applies to your work, and, think about it, whilst a place of worship, it is also a workplace for the minister, he/she almost certainly gets paid to be there, in some form.