Heat the vegetable oil in a large heavy-based saucepan over a moderate heat. Add the beef and sauté for about 5 minutes until browned all over. Remove the beef to a plate, using a slotted spoon. Keep warm.
Add the onions to the pan and cook gently for 5 minutes, then stir in the sliced mushrooms and cook for a further 4 minutes. Return the beef to the pan. Stir in the carrots, barley, stock, wine and seasoning and bring to the boil.
Reduce the heat, partially cover the pan and simmer for 1–1¼ hours, or until the beef and barley are tender.
Stir in the peas and cook, uncovered, for 5 minutes. Add the lemon juice and stir before serving.