This is exactly the dilemma that collectors find themselves in. In the absence of a civilian FFE regime exactly who can certify an article to be FFE?
My view is that in order to satisfy our obligations (duties) under various pieces of legislation the best option is to self certify as Paul has done.
It may be better re-inforced by having some "legalese" wording on the datasheets. I'll look at some options and post them.
Your esteemed leader Spotter is actively looking at a recognised registration scheme. Stay tuned.
In my personal opinion self certification is useless and will weaken your entire approach. Any professional, bomb disposal, LEO, etc is going to immediately ask the same questions as raised here, "who certified". The second that they hear "self certified" they will ask your qualifications, upon hearing "collector" you are done.
There are many individuals that post on this site that are extremely knowledgable, at least in limited areas. There are also others that are idiots, digging items which they have no idea what they are or the damage that they can do, asking questions only after the fact. The same people often examine items and determine them to be safe and inert, with little or no understanding of what components were there in the first place. Self certified? Get real.
If you are going to try and do this for yourselves (UK) you need to establish a certifying board, show some sort of credentials, and get it recognized by someone. Then only recognized members of the board can certify. Otherwise you will have no credibility in the field, where you need it the most.