Lazy payer

I have a tenant who is continually late in paying rent. He is renting a room in a house and should pay weekly. He gets an allowance from the council for £60 per week and get this every fortnight.

He's moved his girlfriend in with him without my permission but its the continual late payment and the amount of effort I put into chasing this payment that is starting to become a real annoyance. The questions I'm asking you are;

1. How many weeks does he have to be in arrears before I can get direct payments.

2. What can I do about making an adjustment to the rent for his girlfriend moving in?

Thank you.