Crush the peppercorns, mustard powder, thyme and celery seeds together with some salt, using a pestle and mortar. Stir in the oil, then rub it all over the beef. (If you have time, cover and chill the joint overnight to marinate. Bring the beef out of the fridge 1 hr before roasting.)
Heat oven to 190C/170C fan/gas 5 and sit the joint in a snug-ish roasting tin. Roast for 12 mins per 450g/1lb (about 55 mins for a 2kg/4lb 8oz joint) for medium-rare, or 15 mins per 450g/1lb (about 1 hr 10 mins) for medium-well.
Remove from the oven, lift onto a platter, cover with foil and rest for 30 mins. If you’re making the Yorkies (p90), increase oven to 220C/200C fan/gas 7.
For the gravy, pour any juices from the roasting tin into a jug. Let the juices separate, then spoon 2 tbsp of the fat back into the tin – if there is no fat, use 2 tbsp butter instead. Discard any other fat. Sit the roasting tin on the hob and stir in the flour, stock cubes, onion chutney or marmalade and Marmite. Cook for 1 min, stirring well to scrape up any beefy bits stuck to the tin, then gradually stir in 750ml hot water from the kettle. Bubble to thicken to a nice consistency, then gently keep warm until ready to serve with the beef, carved into slices.