It depends on the university and course that you're applying to. All of the universities that I have applied to have stated in emails that the actually require x number of merits/distinctions at level 3, whilst I have seen some people on TSR getting offers that specify just an overall Pass.
Generally speaking, the more prestigious the university and the more academic the course, the more credits at merit/distinction that universities are going to require.
Some universities have provided their typical offers for Access students to UCAS and if you do a search on the UCAS website for the specific course, if it has a full entry profile, you might find the requirements there. Otherwise, your best bet would be to email the universities individually and ask for clarification on their entry requirements.