Put the diced lamb into a large bowl, add the flour (1 tbsp) and a pinch of salt and toss the lamb in the flour until it's fully coated.
Peel and roughly chop the onion, carrot and swede. Chop the potatoes into large chunks (a similar size to how you would make roast potatoes, there's no need to peel them).
Heat the butter (1 tbsp) in a large oven-proof saucepan over a medium-high heat. Add the lamb and onions, cook for about 5 minutes until the lamb has browned and the onions are soft. Turn off the heat and add the carrots, swede, pearl barley and lamb stock. Strip the thyme leaves and sprinkle those in too. Give everything a stir then lay the potatoes on top. Season with salt.