Preheat the oven to 180°C/Fan 160°C/Gas 4. Place the beef into a roasting tin just larger than the meat. Lightly crush the peppercorns in a pestle and mortar then mix with 1 tbsp mustard, 1 tbsp olive oil, thyme and seasoning. Rub on the meat.
Roast in the oven for 1 hour for rare, or until cooked to your liking. Remove from the oven and leave covered in foil to rest for at least 10 minutes before preparing the peas.
Skim off as much fat from the roasting tin as possible. Place the tin containing the cooking juices over a high heat and add the wine. Stir well to release any pieces from the base of the tin and bring to the boil. Add the peas, bring to a simmer and cook for 2 minutes or until just tender.
Rip the basil leaves roughly and discard the stalks. Stir the remaining mustard and oil, vinegar, sugar, shallot, and basil into the peas. Season and serve immediately with the beef and any resting juices. Delicious with new potatoes and creamed horseradish.