Well I sold it, and the only game I could fins for it (Neo Geo Soccer) to GameStation for £23... Not to shabby I thought...
Guy told me to hang onto the other clamshells, as Dark Realms is "a quality game" and will sell for quite a bit in clamshell, as will Metal Slug - First Mission. And that Bubble Bobble in clamshell is very rare, as its usually part of a collection... So I'm a hunting for the carts... (so I can feed my PSP habit...)