I know of at least one very large high street company whose policy is not to give a reference at all.
Makes it very hard on someone trying to move on. It is especially hard when the company are actually very happy with the employee, but still can't give a reference.
It is also not always advisable tor a colleague to give one - in my job, my line manager is not allowed to give an employers reference, though she can give a personal character reference. Only the top boss can give an employers reference and use the headed notepaper.