he is a professional grifter.
he is not allowed to practise law, having chosen not to renew his practising certificate.
while there is nothing untoward about a barrister doing this, and there are plenty of noble professions for unregistered barristers (law lecturer, say), he now spends his time on GB News and podcasts with the likes of Liz Truss, bleating about the concerns of the (far) right.
he also boasts of his rapidly increasing twitter follower count.
he is a commercial barrister, and is presumably well-qualified in that area, however he now posts mostly about criminal law (free the right-wing rioters, lock up the left ones, lock up the asylum seekers), and when he frequently makes basic errors (which a pupil barrister should not make, albeit that by his stage in life he may have forgotten the relevant law), he invariably blocks the legal professionals who correct him.
as a barrister he would be able to file a civil claim against Chiltern easily, or make a criminal complaint. Instead he prefers to post "I am bruised" on twitter.
Chiltern's security guard may or may not have acted wrongly, but Barrett appears unlikely to ever act in a way that would allow us to find out which it is.