Preheat the slow cooker if necessary; see the manufacturer's instructions. Heat the oil in a frying pan, add the beef a few pieces at a time until it is all in the pan, then fry over a high heat, stirring, until browned. Remove the beef with a slotted spoon and transfer to the slow cooker pot.
Add the onion to the frying pan and fry, stirring, for 5 minutes or until lightly browned. Mix in the flour, then add the root vegetables and beer and bring to the boil, stirring. Pour into the slow cooker pot.
Add the stock to the frying pan with the herbs and a little salt and pepper, bring to the boil, then pour into the slow cooker pot. Add the pearl barley, cover with the lid and cook on low for 9–10 hours until the beef is tender. Serve with herb croutons (see below), if liked.