Dissolve the stock cubes in the boiling water.
Add all the remaining ingredients apart from the parsley, salt, and pepper, to a large saucepan with a lid. Pour over the stock.
Mix well, set on a medium heat, and bring to the boil. Lower the heat and simmer covered for 1 hour.
When all the veg is cooked and the pearl barley is tender, remove a couple of ladles of veg and stock, then blitz it in a food processor — or use a stick blender until it's smooth.
Add this back into the soup and stir. This will thicken it slightly.
Season to taste with salt and pepper, sprinkle over the parsley, and serve!