In the UK I'd always been told you had to give a reference, usually by phone, and couldn't say anything negative but would just say "she worked here" if the employee wasn't very good.
One day at a small company I worked for the phone rang and a fellow developer answered. He said "the CEO's in a meeting right now, can I help?... Oh Andrew? He was terrible, couldn't code his way out of a cardboard box and he was really hard to get on with. I couldn't stand him personally... Ok, you're welcome, bye". My mouth was on the floor, I'm pretty sure Andrew didn't get that job.
One day at a small company I worked for the phone rang and a fellow developer answered. He said "the CEO's in a meeting right now, can I help?... Oh Andrew? He was terrible, couldn't code his way out of a cardboard box and he was really hard to get on with. I couldn't stand him personally... Ok, you're welcome, bye". My mouth was on the floor, I'm pretty sure Andrew didn't get that job.