Are your job applications hitting a blank wall? If you find that brilliant credentials never land you your dream job, it might be worth checking the quality of your references.

Teachers are particularly vulnerable to bad references, according to John Meredith, principal industrial relations officer at the National Union of Schoolmasters Union of Women Teachers. “The problem is what heads say over the phone,” says Mr Meredith. “It’s very common for them to ring each other to discuss job candidates.”

Unfortunately, verbal “off the record” comments are hard to track down and even harder to correct. The workplace campaigning body, the Work Foundation, says that employers should not express an opinion unless they can show objective evidence to support it. But unless you have bugged the head’s office, it may be impossible to find out whether unfair comments have put off a potential employer.

One irony for teachers is that those with a good record may get a “bald” reference with only basic details provided because the head doesn’t want to lose them, according to Ken McAdam, member adviser at the Association of Teachers and Lecturers.

Another disadvantage is that references are taken into account far earlier in the selection process than in other professions where they will usually only be checked once the selectors are seriously considering offering a job.

“In practice, most schools consider references at an early stage; governors are not experts in selection procedures and often look at references for guidance,” says Mr Meredith.

Written references are easier to challenge. Some local authorities have an “open reference” policy which gives employees the right to see their references. But contrary to popular myth, the Data Protection Act does not give you the right to see your reference if it was given “in confidence”.

You may ask a potential employer if you can have a copy, but they are entitled to refuse unless the writer of the reference has given permission.

Yet employers do not have carte blanche to mislead. The High Court has several times confirmed that employers have a duty to provide a reference which is “true, accurate and fair” and which does not give “an unfair or misleading impression overall”.

Employers who provide inaccurate references can be sued for negligence.

Employers are also on dodgy ground if they include complaints in the reference which the employee is unaware of and has had no chance to comment on. The Employment Appeals Tribunal has indicated that employers should inform people of criticism about their work before this is included in their reference.

So what can you do if you suspect that a negative reference is fouling your career? Mr McAdam suggests that you approach your headteacher in a friendly and open way and ask to discuss your reference. You can explain that a supportive reference is very important to you, and that you are happy to discuss any concerns regarding your performance.

You could also use the debriefing session following an unsuccessful interview to ask about your references. If they are unflattering, the school you are applying to will often be prepared to drop you a hint.

But if you catch sight of your reference on the school secretary’s desk, or even in the photocopier - which is more common than you might think, according to Mr McAdam - contact your union immediately if there are libellous or inaccurate comments. Unions will help members to take up the issues with the headteacher.