The ruling is that you can apply for permission to take your child out of school for up to 10 days in any school year. It is up to the individual school do decide whether or not to grant permission. The school will look at things like the child's attendance, schoolwork, forthcoming exams etc. The secondary school my daughter attends only grant permission in exceptional circumstances in Year 11. If permission is refused and you take the child out of school anyway, the attendance will be recorded as unauthorised. This could be mentioned in a refernce from the school if your child applies for a job and will certainly be mentioned on any college/6th form application. You can also receive a �50 fixed penalty ticket.
I would suggest you have an informal chat with the school beforehand. As spudqueen says, year 11 is THE most important year in a child's education.