Jackie Evans*, a special needs teacher for 20 years, was on holiday when she got a call from her headteacher. A complaint had been made by another member of staff about her disciplinary methods.

It had never happened before and Evans felt it was blown out of proportion. “They did an investigation and it was obvious they weren’t going to drop it. I was terrified they were going to sack me. I didn’t know how I was going to feed my kids.”

Evans’ solicitor advised that, to save her career, she sign a confidentiality clause, known as a non-disclosure agreement (NDA). She left her job with a payout of £8,000 – half of which went on legal fees – was forbidden to disparage her former employer or acknowledge the existence of the agreement, and a reference was agreed.

The week before the complaint Evans had spoken to academy trust leaders about inadequate funding for pupils with special educational needs at her school, and suggested the leaders had not visited often enough in the past 12 months. If Ofsted asked, she told them, the school could get a worse grade. “After that, they were out to get me. My biggest lesson is to put a complaint in writing – I’ve no proof that’s why I was forced out.”

The nightmare didn’t end when she left. Her former head told other schools he would not re-employ her, and while her solicitor has advised taking him to court, a new school would first have to say the poor reference cost Evans a job offer.

Disappeared: the headteachers sacked and gagged by academy trusts Read more

“One school won’t speak against another, so there’s nothing I can do,” she says. “Teaching is my identity. All my other references have been outstanding. My two years in that school has ruined my career.”

A public debate is raging around non-disclosure agreements. Advice for schools, academies and local authorities, published last year, says settlement agreements may be used to end an employment relationship, but that “the law is clear that confidentiality clauses cannot be used to prevent someone from making a protected disclosure, ie whistleblowing”.

A rise in “gagging” clauses has led the Commons women and equalities committee to recommend last month that “NDAs are not used to cover up discrimination and harassment”. Last month, Labour was criticised for its NDA policy on whistleblowers. And the government has now pledged to change the law so people signing NDAs can disclose information to their lawyers and get independent advice. Any NDAs that don’t follow the new requirements will be void.

But will this help teachers? Amanda Brown, deputy general secretary of the National Education Union, which helps members negotiate their settlement agreements, says: “The most valuable part for teachers is often the reference, which is tied into the settlement agreement. That’s where the power imbalance occurs.”

NDAs have become more restrictive, she says, no longer only forbidding an employee from discussing their settlement money, but stopping them from discussing its existence. “That makes it difficult to explain to a new employer how the last employment ended.” As long as employers hold a teacher’s reference, many will be too afraid to call out unfair practice.

Employees who break an NDA are protected in law only if they whistleblow on certain “protected disclosures”: a criminal offence; failing to comply with legal obligations; a miscarriage of justice; endangering health and safety; and damage to the environment. This narrow definition doesn’t cover cheating, discrimination or bullying.

Matthew Wyard, an education barrister at Sinclairslaw, says: “It may be that the categories of protected disclosures need to be broadened, to provide protection in those grey areas that cross between morality and legality”.

Rebecca Dobbs*, a senior school leader, knows of one academy trust in her area that removed “almost all the senior leaders” at a school because they had disagreed with the trust about breaches of exams rules. “I’ve been told by staff who had to sign NDAs that some pupils sat their maths GCSE in the head’s office and were fed answers. Their NDAs state they mustn’t say anything,” she says.

‘Sacked from the school I loved’: a headteacher’s story Read more

Wyard points out that whisleblowing laws don’t cover the issue of cheating, although in practice, staff could alert Ofsted. However, the teachers Dobbs knows are too afraid to do so, for fear of being pursued in court if the claim is unproven.

Discrimination is also a grey area. Pran Patel, an education consultant, recently blogged about an incident he once encountered in a school when he found a teacher crying with “marks on her wrists” after her headteacher had grabbed her during a disagreement. The teacher, a woman of colour, was too afraid to pursue discrimination charges and signed an NDA.

“This is not justice,” he wrote. “This is oppression.” Following the blogpost, Patel says 24 teachers contacted him to share their own experiences of NDAs.

One was Tracey Bourne*, who felt she had been victim of maternity-based discrimination after her request, while pregnant, for a violent pupil to be removed from her class was ignored – only for the pupil to punch a colleague in the stomach. After judicial mediation she signed a £50,000 settlement agreement, which was dependent on her resigning. “The confidentiality clause includes not referring the headteacher to the Teaching Regulation Agency,” she says. Such a referral could have resulted in the headteacher being barred from the profession.

Shockingly, the TRA, the profession’s misconduct regulator, is not on the list of official bodies to which teachers can whistleblow. Stephen Woodhouse, employment law solicitor at Stephensons, says this omission means heads can legally forbid staff from going to the TRA. The law, he says, needs to change. He is backed by Woodhouse: “It’s appropriate that an entity which regulates a profession, such as the TRA, ought to be listed.”

Teachers can report concerns confidentially to the Department for Education. A DfE spokesperson told the Guardian that “in no circumstances should non-disclosure agreements be used by school leaders to stop staff reporting incidents such as bullying, discrimination or sexual misconduct”.

One academy trust boss, who did not wish to be named, says NDAs can also help disgraced practitioners to continue working in schools. In a previous role at a well-known academy trust he saw a senior leader accused of “assessment malpractice” get an NDA instead of being properly reported to a regulator. “That situation in my eyes is completely immoral”, he says. “That person is now in a headship elsewhere.”

But no one is looking at these abuses, because trustees of academies, or governors, are, unbelievably, not required under any guidance or legislation to be informed about NDAs or check how they are used. Emma Knights, chief executive at the National Governance Association, says she “would expect the chair of the board to be used as a sounding board” – but acknowledges there’s nothing to enforce this.

So will the new protections be enough? Given the loopholes, lawmakers may need to think again.

*Names have been changed