meowfood,
the university ask for 2 references, preferably academic ones. I asked 2 lecturers and both said they would, unfortunately only 1 actually obliged (and that took 6 weeks!). The 2nd lecturer was not available when i tried to chase him up so i asked the Admissions department if they would accept a reference from my boss. They said yes and he submitted it within a few days.
My advice is:
* give your lecturers plenty of time to complete the references, especially if you're applying in summer when people are not always around
* don't rule out using a non-academic reference, though if you do, provide the referee with the guidelines (in the case of manchester it's the Referee Report Form) so they can tailor your reference for Academia
* send thank-you notes!