I would recommend the library - some universities have a scheme whereby 6th form students are given free reference access to the university library at certain times of the year. For example, I live in the North East and was allowed to use the Newcastle University Library in my final year of 6th form - though personally I took advantage of books relevant to my course to do some wider reading, there was also plenty of desk space with plug sockets for me to revise. Public libraries are also good places to work, I've just mentioned this because university libraries often have more flexible opening times (luckily for me mine was 24hr). The only thing to consider is that university libraries may not let you in over the university exam period.
If libraries aren't for you, maybe you could meet up with a friend doing a few of the same subjects as you to revise together? Make sure you aren't just going to chat and neglect your work though.
These tips are useful for holidays/study leave etc, but don't forget that there will hopefully be some places at school for you to study when you get back. I was often in your position, so I found it helpful to stay after-school/come into school early, find a quiet spot and do all my studying there. That meant that I could get all my work done and fully relax when I got home, though I know this isn't always logistically possible for everyone to get home afterwards. If you're on study leave, remember no one's stopping you from coming in when you don't have exams just to study.