One very nitpicky point I would like to address with
@Joe96 is that there are other school qualifications within the UK other than A-levels and GCSEs.
There are (although the government is trying to reduce/ eliminate them) - mainly vocational (but also the International Baccalaureate) but there are tables of 'equivalents' although even these are debateable within Education. I can't identify where one is - if you are interested, you could try the UCAS website. The same happens at post 18 level. In this, and any other case, I believe anyone who has a qualification - particularly vocational qualification - that is not listed but they believe is equivalent to GCSEs, A-Levels, degrees etc should claim that they have qualifications at that level. Most of the forms you fill in are anonymous and it is time we valued vocational qualifications in this country (probably worth more than a pass degree in Medieval literature from the University of Avon, formerly Crampton Hodnet Poly*).
* - no offense intended to the people of Crampton Hodnet or to those who have qualifications from polytechnics, which provided excellent, even outstanding, vocational education, but why are some now branching out into low-level courses in traditional academic areas which may diminish their standing? Rant over.