Hi Neil,
Welcome to the forum!
The AWAC licence is about £10 for the year.
you can get them from the big coffee shop at birkenhead park or I'm lead to believe you can get them from local tackle shops.
As for the barbel I would think a ncie fishmeal based groundbait along with pellets over the top should bring them in but I have only fished BH park once and I didnt catch any barbel, mainly tench, roach, rudd etc.
If Barbel are your quarry however you could try lingmere in moreton as they have a very good stock of them going up to around 7lb on the match lake and they fight like demons!

Nice block of luncheon meat/spam down the side should get these out just make sure your gear is up to it!
Hope this helps and tight lines!
Ste