This is just my personal observation from frequenting a few UK detecting forums during the course of the year. If you want a capable detector for the UK, it should be able to deal with iron, and sometimes a lot of it. The most popular detectors are VLF's with fast recovery speeds and good iron discrimination for working disturbed/undisturbed soil full of iron junk (especially ploughed fields).
By far the most popular detector in the UK is the XP Deus, and its forte is picking out thin low conductor targets from amongst iron (hammered & gold coins/artefacts). The AT Pro is also very popular for its iron discrimination, fast recovery speeds and weatherproofing. The CTX3030 & Etrac are popular for detecting undisturbed ground for the deeper targets with with more reliable target ID's, though less capable on the very thin low conductor coins.
There also seems to be a few that run a combination of the CTX3030/Etrac and Deus, depending on the area/ground type, and coins that are targeted. Both machines have their strengths and weaknesses, and tend to compliment each other due to their unique abilities. If intending to hit the beach over there, the CTX/Etrac would be more capable options over the Deus.
In saying all that, there are plenty of other VLF detectors on the market that should prove just as capable, and on a lesser budget if that is a limiting factor (thinking Racer, Fors Core, Goldbug Pro/Teknetics G2, Tesoros, Minelab x-terras, etc.) It isn't unheard of to see large hoards and good finds from budget detectors like the Ace 250 and EuroAce, though more of a case of being in the right place at the right time.
A PI detector with little or no discrimination could prove to be a nightmare in such iron infested areas, unless specifically searching for deep hoards. If you were to use a PI detector, I'd be looking at a Whites SL/TDi with switchable conductivity for some sort of discrimination capability.
