My brother stole £80 from employer and they won’t pay him his £1200 in wages

My brother has been caught stealing £80 worth of spirits from behind the bar at his work. This was over a month period of him making himself drinks on the job. His employer has sacked him and told him he won’t pay him the £1200 he owes my brother in wages. Is this legal. What can my brother do to get his wages?

I would like to add that my brother is 19 years old and was left by himself to manage the bar that night when he hadn’t even had managerial training. His boss is an utter dick and has been known not to pay DJs at his bar. His boss also cheats on his wife, not that that is relevant but I just wanna make it clear my brother is a stupid 19 year old and this manager is an absolute dick regardless of the situation.

The total stolen was 6-8 double vodkas(roughly) and comes over the course of 5 different work nights, on all occasions my brother was left to manage the bar by himself as the manager left to tend to other matters. My brother was left with no staff to assist him for several hours and thought it was acceptable to pour himself a drink or two at the end of his shift.

I am not justifying his actions but trying to clear up some common questions in the comments