My girlfriend is a 17 year old Tutor in the uk. She has a “0 hour” contract which I believe means the company she works for asks her to come in whenever there is work for her. A few days ago she was asked to come in for the day and one of the hours she was there, none of her scheduled students turned up meaning she had no one to tutor. She has been told they aren't going to pay her for that hour. Is there a rule that says she should have been considering that they asked her to come into work for that hour and she did?