would go in tomorrow as usuall .. then on monday phone area manager and ask politly if he wants to loose you to another company who have already contacted you with a reasonable offer ...
see what his reaction is ..
if he says piss off then politly tell him you will hand in your notice asap..
if he says what will make you stay outline all the problems you have . and give him a deadline to comeback to you about getting them resolved. politly ask for it in writing to confirm the converstaion.
tell him you will be working to the legal guidlines set out about working hours etc refer to your contract about your working hours and ask him what he will be doing for cover when you are on your breaks.
give him reasonable time to return with answers about how he can make your job better 1 week should suffice .
see what happens after that ..
but always be polite and do not get stressed out about it all as if you have to resign its always nie to get some form of reference from a previous employer.
dont forget the area manager has to report to someone aswell .. might be worth jumping him and going higher.