In a large bowl, stir together the milk, sugar and yeast with 170ml warm (not boiling) water, then rest for 10 minutes.
In a small bowl, combine the flour and salt. Add this to the yeast mixture then, using a whisk, beat for 5-7 minutes until it is smooth and lump-free. Cover with a clean kitchen towel and leave on your oven top or somewhere warm for 90-120 minutes.
In another small bowl, mix the baking powder with the bicarbonate of soda. Add 1 tbsp boiling water and pour into your batter, gently stirring as you do. Once the mixture has combined, set aside for 30 minutes.
Meanwhile, grease a few chef rings with the oil using a pastry brush, then lightly oil a large non-stick frying pan. Place the oiled chef rings into the pan, then gently heat over a medium-low flame for 1 minute. Carefully half fill each ring with the batter. The crumpets will need around 9-15 minutes to cook through, and tiny holes should appear as the mixture cooks. They may also start to loosen away from the edge of the chef ring.
Once cooked, use a butter knife to ease free from the rings, then use kitchen tongs to take the chef rings out of the pan. Keeping the large pan on a gentle heat, flip the crumpets on to their uncooked side using a spatula. Cook until golden brown on both sides, then cool on a wire rack. Repeat until you’ve used up all your mixture and serve warm with toppings of your choice.