Hello mate!
First you need to get in contact with your nearest police station and ask them to send you out some FAC application forms. Then arange to have a meeting with your local FO ( firearms officer). He will help you through all the forms and advise you what to do. The police are genearlly more leneant towards FAC air rifles than rimfire. As they are less likely to have a huge over travel if you miss your target. I have a FAC air rifle in .177 and to be honest it isnt worth the decreased shots per charge of air. You would be better of going for a .22 rimfire, i also found it easyer