Uncertifed stuff can be shown at clubs and such thats why the IFI and various film festivals sell memberships so the tickets can be called memberships so thats not really an issue the issue is getting permission from the makers to show unlicenced stuff and they arent likely to give permission to show fansubbed versions of their shows
Most Japanese companies (with a couple of exceptions) don't have major issues with screening fansubs of material not licenced in the US/UK. (at least, none of the "we're going to sue your ass" kind).
It certainly is illegal to show fansubs under the Berne Convention and other worldwide copyright law, however it is commonplace to show them (basically every UK Anime convention, rightly or wrongly, shows *vast* amounts of them).
Be careful about showing stuff that has been licenced in the US, but not in the UK. ADV Films in particular can be a bit thorny about that issue..
I'm not familiar with the law regarding classification in the RoI so unfortunately cannot comment on its implementation - however for example, at Q-Con I have taken the decision to screen *only* material that has been officially rated due to:
1) It is illegal in the UK to show unrated material, outside of certain special criteria
2) As the convention is a fairly 'public' event, and allows minors, screening only material which has been officially classified removes any comeback if "little johnny' gets offended by something he watches - any issues arising go to the classification body, not us.
3) Uncertainly over wether showing unclassified material may affect our events insurance coverage.
I honestly can't say how many of these issues affect EirtaKon, however it might be worth considering their impact (and then chucking them aside ;)
Richard