I've been with a company for a little over a year. Gross pay is between 2 and 2.5k. Never signed any contract or confirmation for employment. How long notice period do I need to give? Would 1 to 2 weeks be sufficient?

If my resignation letter were to say 1 months notice, and my employer verbally agreed to allow me to leave say 2 weeks earlier, if later he decided to play dirty would I be liable to reimburse that 2 weeks period?

Thanks