i'm self employed and the only way i could work for another company in my trade is if i "sub contracted" my self to that company wich you would have to pay your own N I contributions. the tax you might have to pay unless he gives you a tax voucher then the tax is already paid by him. to do this you would need a CIS card. the good thing for him is if he didnt want you to work for him he wouldnt have to sack you , the bad thing for you is no sick pay , holiday? and theres not work 100% guaranteed