I'll revive this with a little of what I know on the matter as a lifelong angler and once time Head Bailiff for a fishing club..
Virtually any freshwater (coarse) fish, if not all, can be eaten.... if you're hungry enough
There are obviously some that are far better eating than others.
Pike tend to be pretty bony, but get past the bones and the flesh is good tucker. I like it made up into fishcakes so as to get around the bones problem.
Perch can actually be far better than trout if you (a) get a good 'un (over a pound), (b) get it from a clean running river, not a muddy little pond, and (c) cook it well without over cooking it. Perch has a firm white flesh and tastes good.
Taking freshwater (coarse) fish from a water can lead you into all sorts of difficulties with the Law though. Most waters are controlled by a club, fishing organisation, or the landowner of the banks. In order to take fish for the pot legally you would have to have sepcific permission from the controlling person/club to
take (kill) the fish you caught as most, if not all clubs have within their rules the fact that all fish must be returned to the water alive. Taking fish without this express permission can lead to court case for
theft if you are caught. Being a member of the club (or buying a "Day Ticket") in order to fish will mean being bound by the club rules.
Some waters are 'free fishing' and do not come under the control of anyone (other than the local council in most cases). If taking fish from these waters, I'd advise you to check on any local by-laws regarding the matter as they vary from place to place around the country.
Whether fishing club controlled waters, or in 'free fishing' areas, you MUST still be in posession of a valid Rod Licence (issued by the EA and available from Post Offices or online) before fishing. Being caught fishing without one can result in fines of thousands of pounds and a criminal record.
If you are fishing for Game Fish (trout and salmon) you must have the appropriate rod licence to do so.
Having bought your Rod Licence, you are then bound by the rules and regs concerning the methods of taking fish. These basically limit your legal fishing activities to the use of rod, line, and hook only (other than in the case of eels). No netting, poisoning, gaffing or 'snagging', no setting of night (set) lines either.
That's a basic run-down of the law on freshwater fishing in the UK as I understand it. In order to stay within the law it basically means that you need at least one licence to fish anywhere at all, you may only do so with rod and line, and you may well have to return all you catch (other than Game Fish).