http://www.brightknowledge.org/ careers, higher education study issues, a good general website
https://www.ucas.com/alternatives/gap-year/gap-years-ideas-and-things-think-about
Below are some suggestions of volunteering sites (there are many available just do an internet search)
https://volunteeringmatters.org.uk/opportunity/full-time-volunteer-opportunity-all-over-the-uk/
https://www.royalvoluntaryservice.org.uk/volunteering/students-young-adults-volunteering/
https://www.beanstalkcharity.org.uk/pages/category/about-volunteering