thanks for the discussions,
1, there should be RCD in the main switch box and I don't have it, is it correct? if so I will find an electrician to install one, is it an expensive work?
2, even though the small separate RCD box for SWA is off (I can lock by someone suggested above), but it is still not safe, I need to physically disconnect the cable inside the box, is that correct?
thanks, always good to learn something new