Roast lamb rump with flageolet and spring veg ragout

Name: Roast lamb rump with flageolet and spring veg ragout
Ingredients: 250g dried flageolet beans; 1 tbsp of each unsalted butter and olive oil; 4 (about 200g each) Gower salt marsh lamb rumps; 1 onion finely diced; 1 large carrot finely diced; 2 sticks celery finely chopped; 1 bay leaf; a few sprigs thyme; 2 tbsp tomato purée; 200ml white wine; 500ml chicken stock; 150g baby broad beans blanched and podded; 150g frozen peas defrosted; 1 tbsp coriander seeds; 4 tbsp extra-virgin olive oil; 2 very ripe tomatoes finely chopped; ½ a small bunch basil leaves picked and shredded