I'm fortunate enough to live near a branch of Booth's and their CKs have been my preferred choice for several years, although I'm sure they're smaller than they used to be. I admit I never buy them at full price. Otherwise, the Morrison's ones at about £3.35 for two were almost as good. Very buttery and garlicky. I haven't seen them locally recently.
I always oven-cook them but I remember the likes of Berni and Cavalier Steak Bars used to deep-fry them. As if they weren't unhealthy enough!