Cook the pearl barley in a large saucepan with stock for 45-50 minutes, or until soft. Drain and set aside to cool slightly.
Heat the butter in a large non-stick pan and cook the onion and celery for 2-3 minutes, or until soft and slightly coloured.
Add the remaining stuffing ingredients to the pan and mix well.
Using the stuffing in a rolled shoulder of lamb or crown roast.
Tip: Alternatively, transfer the stuffing mixture to a large rectangular ovenproof dish and bake for 20 minutes at Gas mark 4, 180°C, 350°F and serve as an accompaniment with roast beef or lamb.