Crumpets are one of the simplest baked goods, consisting of little more than flour, a liquid and a raising agent. As with most cookery, experts and enthusiasts have a wide range of views on the best or correct way to make a crumpet. However, the variations do fall into some distinct categories.
"English crumpet" is simply another term for what many people would think of simply as a "crumpet". The general crumpet baking process is consistent among recipes: mixing the flour and liquid, a proving stage, adding a raising agent, a second proving stage, putting the mixture into rings, then baking. The flour can be plain flour, bread flour or a mix of the two. The liquid can be water or milk. The raising agent is usually yeast, though many people add baking powder or bicarbonate of soda to create air bubbles and give the finished crumpets more of their characteristic holes.
Some commercial manufacturers produce square crumpets for retail distribution. The content and baking of these crumpets is usually identical to that of traditional crumpets, but using a square "mould" rather than a ring. The practical benefit is that the crumpets have corners and are therefore easier to remove from a toaster.
In British English, "pikelets" are simply pancakes that are made without any form of "mould" such as a ring. This means the batter spreads out during cooking. The result looks and tastes like an English crumpet but is thinner and wider across.
A Scottish crumpet is a completely different food to a traditional or English crumpet. It's a variation of the Scotch pancake, which itself is like a traditional pancake but a little thicker and with fruit added to the batter before cooking. Unlike a Scotch pancake, a Scottish crumpet is only cooked on one side, usually by frying. This means the side that isn't directly exposed to the heat tends to bubble up and produce holes, hence the use of the term crumpet.