If they are still relatively young their school/college will hold exam result information. The prospective employee should be able to get a letter from their school with that info. I imagine a university would do much the same. Copies of certificates are expensive to get from the boards
Sorry - been out. Vocational qualifications like NVQs etc. are done through a college so their exams and qualifications department would be able to supply the information. Again it's unlikely that they would divulge that to you but your employee can get a letter. (I had to do this for my son who lost his certificates)
Do you need to check them? If they want a job/place on a course that requires evidence of a qualification, isn't it their responsibility to provide this evidence or risk not getting the place/job? They can get GCSE/GCE certs from the AQA http://www.qca.org.uk/qca_4521.aspx