It seems really unprofessional, he should be giving you proper training, and should have taken your details/proof you are allowed to work in the UK/bank info BEFORE you started a shift, and then discussed with you personally any issues he has. The best thing you need to do is go in and discuss with him what is going on. If he doesn't want to hire you, it's his loss, because honestly it's probably a lucky escape that you aren't getting messed around more by an unprofessional employer. Make sure you chase up about getting paid too, just in case! If you get too much hassle, visit Citizen's Advice and look into taking this further.