Headteachers have the discretion to grant leave, but they should only do so in exceptional circumstances. If a headteacher grants a leave request, it will be for them to determine the length of time that the child can be away from school. This leave is unlikely, however, to be granted for the purposes of a family holiday.
Parents can be fined for taking their child on holiday during term time without consent from the school.
Find information on school term times and holidays on GOV.UK.