First heat the milk in a pan until it is just starting to feel hot – blood temperature. Whisk in the Marmite until it has combined completely with the milk – the milk should turn a colour similar to milky coffee.
Remove the pan from the heat and leave to cool down. If you have time, chill it as well, but don’t worry if you can’t.
Mix the flour, baking powder and a pinch of salt in a bowl. Add the butter and rub it in until the mixture is the texture of fine breadcrumbs. Add the grated cheddar cheese, mustard powder and sugar, then leave the mixture in the fridge to chill for half an hour.
Preheat the oven to 220°C/Fan 200°C/Gas 7. Line a baking tray with a parchment-lined baking sheet.
Reserve a tablespoon of the milk and Marmite mixture for a glaze and pour the rest into the bowl of dry ingredients. Mix everything together as quickly as you can, using either a table knife or your fingers.
Don't overwork or the scones will be tough. Turn the dough out onto a floured surface and pat it down until it is about 3cm thick – do this with your hands, no need for a rolling pin.
Dip a 6cm pastry cutter in flour and cut out rounds, pushing the cutter straight down without twisting. Squash the remaining dough together – again trying to keep handling to a minimum – and cut out more scones. You should end up with about 8.
Put the scones on the baking tray and brush with the reserved milk and Marmite. Bake for 12–15 minutes until they are well risen and deep golden brown. Eat these savoury scones hot or cold, with lots of butter.