The Showmasters forum are saying that they are 'involved' but I wouldn't want to speculate on what that involvement might look like.
If this is a CBS licenced event, I think the CBS legal team need to take a little trip to Milton Keynes and get Joiner to STFU. Given his track record of organising anything to do with Star Trek, CBS shouldn't want him going around saying he has anything at all to do with this event.
The actual company that appears to be running the event is called Media 10 Ltd, based in Loughton, Essex. They have a good record of organising the Ideal Home Exhibition and Grand Designs exhibtion. In terms of reputability and integrity, Media 10 Ltd seem to be a million miles away from certain other UK event organisers.
Event most likely to be a convention of some kind. I hope whoever runs it takes note of what's happened in previous years ie no one turns up unless you get the really big guns out. Nimoy's retired, so that's one less of those guns. Fro me, it has to be a full TNG cast reunion for the 25th anni.