Sam Ayre said:

and if it cannot be found then it should be put down as an FI

Are we sure that's the purpose of FI? See my post of yesterday discussing an alternative point of view on use of FI, and the statement in Note 9 of EICR form. Summing up, I guess you're saying an installation is potentially unsafe or not fit for continued use because you couldn't find something (a 'LIM' in some people's view)?

Thank you for your input you've definitely got a wealth of knowledge and you've brought up some very interesting points.

Regarding what you said about a poor connection or a corded connection as you've said and as it's known we tend to work on a sample base which usually only covers a 20% visual inspection. So if on this bases something did happen which wasn't picked up on our visual inspection who would be liable if any injury occured from this or would it be classes as something completely different. 

Sam Ayre said:

who would be liable if any injury occured from this or would it be classes as something completely different. 

We're getting into the legal side of things now, and of course I'm not a lawyer, but I understand that you could only be liable for the truth ('veracity') of what you have said you've done, provided you say that in your contract for doing the work, and provided what you've done is 'reasonable' in the terms of what a 'competent person' would do in performing the contract.

John Peckham  may be able to provide some further guidance based on his experience here.

Liability might arise in at least 3 ways: criminal (e.g. failure to comply with H&S legislation); contract (e.g. you contracted to inspect all sockets, but only did 20%); or tort (negligence).

If you sampled, say 20% of socket outlets and one of the remaining 80% caught fire soon afterwards, it is difficult to see how that could be negligent if the advice on sampling in GN 3 (3.8.4 in my edition) has been followed. So I don't think that you need to worry about that.

Correct me if I am misunderstanding but would that mean that any circuit that we've been unable to identify we would class only as a limitation as from what I can gather from your previous discussions an FI should be used on a known circuit which has a potential to show a C1 or C2 if further investigation is carried out. However surely if where unable to identify a circuit this still creates the chance of a C1 or a C2? 

Sam Ayre said:

However surely if where unable to identify a circuit this still creates the chance of a C1 or a C2? 

How have you risk assessed that? How is it any different to only inspecting and testing a percentage of outlets (or circuits), and one of the socket-outlets you didn't check has a fault shutter mechanism, or perhaps worse has a broken cpc at the rear and therefore is a potential deathtrap?

I could see the point if you had contracted to do 100 % inspection and testing on a simple installation, there might be an issue ... it's definitely a limitation, and you could agree with the person ordering the inspection that it's an FI ... but under those circumstances if the FI is so "urgent" why aren't you looking into it as part of the 100 % testing contract (even if only as a variation) ? At the end of the day, if the circuit is so hard to identify, what's the point of FI? It's an FI that, potentially, could only be resolved by completely disconnecting the circuit.

It's also worth looking at this from the point of view of major infrastructure, or large and complex factory etc. where you won't (can't) testing all of  the installation at each inspection ... and some it perhaps never unless a check is made when the connected safety-related equipment is maintained.

I believe you should always test every accessible socket outlet on the circuit being tested, using R1+R2 tests, which will verify the connection and allow you to inspect them visually. The sampling rate for the inspection over five years is 20% of the socket outlet circuits of the whole installation. So you are not liable if you have not tested or inspected that circuit yet. This only applies to more complex installations. For a domestic property, you need to test everything every time.

I sense a degree of self-contradiction here: "every accessible socket" ... "For a domestic property, you need to test everything every time". What about the socket behind the Victorian triple wardrobe or bookcase?

If a socket is hidden behind a Victorian triple wardrobe or bookcase and cannot be reached for inspection, you should state in part 6 of the EICR that the socket is not accessible.