Buying a sub 12 ft lb air rifle (6ft lb for pistols) is hassle free in England,Scotland however is another matter,I was in Scotland on holiday last year and the one gunshop I visited said that airgun licensing had all but killed his airgun sales to the point he no longer stocked any.
There are no restrictions on the number or type of airgun you can own,there is a good and healthy following of antique/vintage rifles and pistols as well.If you want to up the power and go over the 12 ft lb limit then it has to be aquired via a Firearms Certificate,these are issued by your area Police Firearms Licencing Dept and are only available to those shooters who can prove they have a need for and acceptable land to shoot on with the landowners written permission,you really have to jump through hoops.
I relinquished my Firearms Certificate at the last renewal as I was not doing enough shooting to maintain permission on the land I had available,plus it is now becoming the norm to have doctors written testimony that you are a 'fit' person etc,I didn't feel as though I would miss my .22 rimfires which is one of the reasons I have got back into airgun shooting,much easier access to ranges.