I was in the U.K. a couple eyars ago on business. Picked up a couple guns books in London. From the looks of the ads, it appears that owning the firearm or pellet rifle is difficult. But the suppressors are OTC if you have the firearm. Just the opposite of the U.S. where firearms are easy, but it takes 3 months, a $200 tax stamp, finger prints and a federal back ground check for the suppressor.
It was interesting to see the set ups (ghillie suits, blinds, suppressed air rifles) that were used in the U.K. to pop pigeons in the back yards.