Googled this as I was looking for an answer as more and more races are considered non-official by the UKA. Which is fine for whatever petty inter-body issues they all have with each other, but as runners we have choices on what races we do, infact more and more choice for events in the same areas on the same day, so if given the choice of doing one thats UKA (mainly as im interested in the difficulty ratings they use which can sometimes turn you from being disappointed in a performance, to realising it was on a harder course). And most of us are motivated by continuous improvement, and obviously the better you get, the smaller the improvements are, so having the runbritain data can help with that....
Personally im happy I ran an 88 min half on sunday....but annoyed it doesnt get put on my score on runbritain. Moreso because parkruns are counted, and when I was livng in the US, I could submit the results for races I did out there (obviously not UKA affiliated) and they were accepted! So in context, the Maidenhead Half wasnt good enough for UKA, but the San Jose Half was.
Anyway, if you want to know if a race is "official" or not, you can check the runbritain events calender. If its listed with a race number on there, its official. If its not, you wont get the score. Looks like many races that were UKA in 2011 have decided to go ARC for 2012.
http://runbritain.com/events/