In reply to minus273degrees:
This is something that most clubs face every now and then, my opinion of how it works having gone through it with the uni climbing and kayaking clubs and now working in h&s is...
It's fine for people to use club kit outside club events - it should be signed out to them and they need to be aware that what they are signing for is to say that they have carried out a visual inspection and are happy with the condition.
The best way to cover yourselves if there is a problem (as sadly them saying it looked OK isn't enough to cover you if something does break and they try to sue you) is to have a system of inspection at regular intervals that's recorded so that if something comes up you can show that you've inspected it and argue that you've done all that's reasonably possible for you to do to be sure the kit is safe, if someone who is qualified does this then awesome, otherwise just get the gear secs to and see if you can write down what it is they are looking for in case you need to justify your 'inspection'. The chances of this coming up however is really really really small, such a policy should hopefully cover you legally but will have the advantage of hopefully appeasing your union who are probably just terrified of someone suing them.
The issue of people falling on it, here you have to rely on trust and explicitly state when people take out kit that if they fall on it etc then they must tell you (and point out they could be legally liable for the kit failing in future as a result of that fall if they don't inform you).
And obviously when people take kit out that's not on a club trip then if they damage it they replace it, usually a committee member would check it over and sign it back into the store.
This is all a lot harder if you can't restrict access to the store to committee only though (a problem we had with kayaking) as then people are prone to just take the kit, but by having a strict policy and trying your best to enforce it you're doing all you can really.
This is probably overkill compared to how most clubs operate although is good practice for getting used to how such things work in industry!
Good luck with arguing it with your union, it's a pain in the neck for everyone if you can only use kit on club trips.