Regardless of contract, if you’ve stated that you’re planning on leaving and that you intend your last working day to be, say, 1st December, you’re telling him that you’ll be working there up until that date.
Given that you’ve been there for at least 2 full years (and maybe three) then legally he’d have to offer you one week per year of service, even if he doesn’t want you to be in the office.
However, if the norm for the business is that there’s a month’s notice (which it is for the vast majority of firms) then that’s what he has to stick to.
All depends on whether he’s the sort of person who’ll stick to the law – chasing someone through the courts for a week’s wages is hard work and takes some time. Then again, you don’t like being there and you’re going to come across this same isse whenever you resign.
Do you have sufficient funds to tide you over for a full month should this guy decide to flout the law and not pay you?