Well its strange as 165.6875 been very busy all day again but nothing at all on the other events channel even though they were regularly mentioning using another channel. Its possible I just cant receive the other channel I suppose from my location.
With a bit of luck I can get down to Cardiff in the next few days with a couple of close call radios to solve the mystery.
I will say mind that when setting up for the NATO summit and on new years eve they were using 163.925 with a repeater input on 159.4250 ctcss 192.8 but seems that there is no activity on there at the moment.
It looks like the event is being managed by a company called '11th Hour Events' and possibly they have their own allocations that I have not found as of yet.
Still a lot of activity on 165.6875 but it sounds like they have four channels in use. looks unlikely I will be able to make it to Cardiff this weekend as was originally hoped to track the other frequencies down.
If anyone has info regarding '11th Hour Events' please let me know - cheers.