Noisy tenant

Tenancy Types and Management

I have a house, converted into two separate flats.
The downstairs tenat has complained about noise from upstairs until about 3am.
i told the upstairs tenant who apologised and said he would make sure it was kept down.
It has happened again, but this time the lad upstairs said that he wasn't in until about 6am and it must have been next door, but I do not believe this.
I do not want to put my downstairs tenant through this, is there any action I can take to evict the upsatirs tenant who is in the first month of his 6 month AST. I must 'nip this in the bud', so if I cannot evect, what firm action can I legally take?

Thanks