Roast beef dinner

Name: Roast beef dinner
Ingredients: 800g/1lb 12oz floury potatoes, preferably Maris Piper, peeled and cut into roughly 5cm/2in chunks; 2–3 tbsp cold pressed rapeseed oil or extra virgin olive oil, plus extra for greasing; 800g/1lb 12oz beef topside, tied (see tip); 2 tbsp cold pressed rapeseed oil or extra virgin olive oil; 1 medium onion, thickly sliced; 2 medium carrots, trimmed and thickly sliced; 2 celery sticks, trimmed and thickly sliced; 2–3 bushy sprigs fresh thyme or ½ tsp dried thyme; 1 large bay leaf; 1 heaped tbsp plain flour; few drops naturally brewed dark soy sauce; sea salt and black pepper