There is often some confusion around this matter, in part because the situation varies depending on who holds the reference, and how it was issued.
While the reference rests with the referee you have no legal right to see the reference
Some schools may have a policy of open referencing (often as part of a broader LA-recommended policy). In such cases, it may be possible to see a reference before or after it has been sent.
In many schools, references are given in confidence to the prospective employer. In such circumstances, you have no right to see the reference before it is sent. However, once the reference has been received by your prospective employer, it is possible to request to see the reference under the provisions of the data protection act. In such circumstances, it may be appropriate for the prospective employer to withhold some information from the employee so as to protect the anonymity of the referee. He may, alternatively, seek the permission of the referee to share the information.
Another common misconception is that it is illegal to provide a bad reference for an employee. In fact, no subjective view is taken by the law. However, an employer does owe a duty of care to an employee to ensure that any reference provided is true, fair and accurate.
This was confirmed by the case of Spring vs Guardian Assurance plc (1995) (See this explanation at BullyOnline)
Is my employer obliged to give a reference?
There is no requirement in law for an employer to provide a reference for an employee, except where requested by the Financial Services Authority.
However, employers are advised to have in place a policy on such matters, which is adhered to for all employees. If an employer refuses to give a reference where he has previously agreed to requests for a reference from other employees, then there is a risk of a claim of discrimination under one of the relevant acts.
Also, in some cases, a contract of employment includes a clause which requires an employer to give a reference