I think people are getting confused with all the different 'foundation' things!
The UAL Arts foundation diploma is a level 3 qualification in Art. It allows people to develop a much broader portfolio for entry to Art college / art degrees than they might otherwise have been able to at school.
A Foundation year of a degree programme is an extra year of a standard degree, aimed at students who didn't have either the right subjects, or the right grades, to gain entry to the first year - it's sometimes known as 'year 0' for that reason.
A Foundation degree is equivalent in credits to a Diploma of Higher Education - the same as the first two years of a standard degree programme. Often there is the option to top-up to a full degree by doing one further year. The only difference between DipHEs and Foundation degrees is that the latter are vocational. So you wouldn't be able to do a FD in Art History - that would be a DipHE, but you can do FDs in Computing, Lab skills etc.