Place the milk and water in a pan and heat gently until just lukewarm. Pour into a Pyrex jug, stir in the sugar and yeast, then leave to stand in a warm place until there is a thick frothy head. Sift the flour and salt into a bowl, make a well in the centre and pour in the yeast mixture. Mix the flour into the liquid, then beat well to form a smooth batter. Cover with a tea towel or cling film and leave to rise in a warm place for another 45 minutes, until light and frothy.

Preheat a large griddle (or heavy-based frying pan) over a medium heat for 5 minutes. Grease four 10cm crumpet rings or pastry cutters thoroughly. Lightly oil the griddle then place the rings onto the griddle and spoon some of the mixture into each, filling them about three quarters full. Cook until bubbles appear on the surface and burst leaving holes, then turn over with a palette knife and cook for 2-3 minutes more.

Transfer to a wire cooling rack and remove the rings. Butter the rings and the griddle before cooking the next batch. Serve the crumpets warm with butter and jam.