A near miss even before you've been recruited, oh no! Seriously though, i was in exactly that position about 3 years back but scraped through at my second effort so best of luck at your next stab. As far as advice for your next comfortable chat, have you spoken to recruitment to ask why you failed?
Invariably it's because either someone has failed to prepare sufficiently (background knowledge of recent NATS history etc), the interviewer was unsure of your commitment to a career in NATS (thus by turning up to the next inerview prepared you might alleviate that belief), or as was my case, you didn't have a clear plan of action when presented with some scenario type Q's.
My suggestion is that when you are given a situation such as 2 aircraft head-on, same level and are asked for your reaction, give only 1. I procrastinated and said i could climb 1 and descend the other, or maybe turn 1 or both aircraft and it came across as indecisive. They were looking for a quick but considered reaction and will often try and make you change your mind to see if you can stick to your guns. If you are then presented with information that makes your original decision less valid then have in mind a suitable alternative, just don't get over eager and give every resolution to the situation you can think of asap!
My other piece of advice is to read through as many threads on this site as you can. Over the last few years, the resources available to newbies has got much better thanks to some kindly folk posting info on a regular basis on this site. You will find loads of info and opinion from people in your shoes or those who have recently gone through selection testing.
Best of luck with your second interview and enjoy Bournemouth when you get there
RP 45