Heat the oil in a large pan over a medium heat. Add the chopped onion, carrots, celery and parsnip. Cook for 5 minutes, stirring occasionally, until the onion has softened.
Stir in the crushed garlic and dried mixed herbs. Cook for 1 minute until fragrant.
Add the rinsed pearl barley, drained mixed beans, vegetable stock and bay leaf. Bring to the boil, then reduce the heat to low and simmer for 25 minutes until the barley is tender and the stew has thickened.
Remove the bay leaf and season with salt, black pepper and a splash of Worcestershire sauce if using.
Stir well and adjust the consistency with a little extra hot water if the stew is too thick.
Serve hot on its own or with a chunk of bread for dipping.