Asking for Permission:
- Yes, please do.
- Sure, go ahead.
- No problem.
- Please feel free.
- Go right ahead.
- Please feel free + infinitive
Refusing to give permission:
- No, please don’t.
- I’m sorry, but that’s not possible.
- I'm afraid that's not possible.
- I'm afraid, but you can't.
- I'm afraid I'd prefer if you didn't / don't.
- Sorry, but I'd rather you not do that.
- Unfortunately, I need to say no.