Can my partner have a job as well as carrying on with his electrical apprenticeship?

So my partner is currently an apprentice for his fathers' self employed business.There have been a few problems though:
- his father doesn't turn up on time in the morning and leaves him waiting for hours to start work
- he doesn't pay him every week, my partner needs money to pay his bills
- he pays him the same wage of £180 a week (when he has the money to pay him) regardless of the hours he has worked
- he takes out his family issues on my partner, for example if he has an argument with his ex (my partners mother)he tells my partner he is sacked. He also threatens to not pay his wages if he doesnt do a personal errand for him.

Recently his father has told him to find another apprentice because he can't afford to pay him.There are hardly any apprenticeships available,this is why my partner hasn't left sooner.
He is really struggling with money as he is not getting payed half the time.He also attends college 1 day a week as part of the apprenticeship.

I was just wondering if he would be able to get another job(i know a place that would except him) as well as carrying on with the apprenticeship with his father.If he accepted this job he would be working monday,tuesday,and thursday,would be able to attend college on a wednesday,he would finish work at 12 friday to have the rest of the day to work with his father,and could also work with him on a saturday.This way he would be earning a decent regular wage,while still working towards the apprenticeship. Would this be allowed?