An FAC HW80 is an option worth considering. They were originally designed to be around 18 ft/lb and can be tuned to 20, but they were modified to reduce power to comply with UK law. The original full power version is said to shoot better than the sub-12 version.
I think they're about £500 new (maybe gone up recently what with the economic situation), but that is a significant saving over a higher power pcp.
It all depends what you want it for. Corvids out of trees at around thirty yards I would think it would be ideal for, possibly in .20 calibre as a compromise for energy and trajectory at that power level.
As
@Fursty Ferret says, the advantage of a top-end pcp with dialable power is that it will cover many bases, and perform the tasks of two or more rifles, from a sub-12 rifle to a high power 40+lb rabbit knocker. But you need fairly deep pockets to start with.
If you haven't currently got any sort of air rifle and would be opting for a pcp even if it is sub-12, a single dialable FAC becomes a cost effective way to go.
I wouldn't be bothered about having an on-ticket gun as my only air rifle. It's no more hassle than owning licensed cartridge rifles and shotguns and in any case it's not inconceivable that all air guns will be licensed across all parts of the UK before long anyway, so you might as well own one with more authority and greater versatility.