They won't know through your NI number, as all this shows is how much NI you have paid, not how many hours you have worked. It might be best to reduce your hours slightly so that you don't risk going over (how did this happen in the first place - is it because you have to 'clock in and clock out?)?...

I am a master student with 18month visa (TIER 4). I started a part time job some weeks ago. I clearly made it clear to my manager that I can't work more than 20 hours. we both agreed, but unfortunately one of my pay slip is showing 20. 40hours. that is almost 21hours. I have decided to monitor the h...