The police watchdog has apologised to a dying mother for investigative failings after she was stripped and handcuffed in a police cell for 11 hours while pregnant.

Lynette Wallace, 46 and from Notttingham, has spent six years since the July 2011 incident seeking redress and is now suing the Independent Police Complaints Commission (IPCC) for a “litany of failures” in the way it investigated the conduct of the police.

Wallace, who has seven children, hopes the legal action can be expedited before she dies of cancer.

Wallace went into labour 10 weeks early following the incident in Nottingham’s Bridewell police station and subsequently had an emergency caesarean in hospital. She had been arrested and accused of arson with intent to endanger life and intimidating a witness but all charges against her were later dropped.

Nottinghamshire police later issued a public apology to her.

Wallace was seven and a half months pregnant with her daughter Charna when she was stripped naked from the waist up, handcuffed for 11 hours and repeatedly punched on the arm by officers while she was in the cell.

Three of the officers involved – an inspector and two sergeants – have been disciplined. All three were found guilty of gross misconduct.

In May this year, a police disciplinary panel decided to take no further action against two other officers involved in the incident because of significant delays in investigating the case. The panel criticised the IPCC for delays in their investigation and said they had provided “no real justification” for these delays.

Wallace said: “I’ve been fighting the police and the IPCC for years over this incident. The police should not be allowed to go around bullying and assaulting pregnant women and their unborn children. Letting these police officers off sends the wrong message. I want to see justice done before I die.”

A Nottinghamshire police spokesman said: “Over the last six years a number of complaints and subsequent investigations have been undertaken in relation to the treatment of a pregnant woman whilst in custody in July 2011. Consequently three officers were dealt with for gross misconduct in 2012.

“The IPCC had directed that a further two officers had a case to answer for gross misconduct. The force convened a misconduct panel to hear the case. After carefully considering the submissions from all parties, the misconduct panel determined that it was not possible to have a fair hearing of the allegations due to delays and significant departures from the regulatory framework. As a result the proceedings were stayed. This means that they have now concluded and the case against the officers will not proceed.”

The IPCC commissioner Derrick Campbell said: “We very much regret our part in the delays in this case and we have apologised to Ms Wallace for the frustration and upset caused. There were some delays over which we had no control but we recognise our investigations took longer than they should have. We fully appreciate that Ms Wallace feels badly let down by the outcome.

“In September 2015, we referred the matter to the CPS who decided not to prosecute in March 2016. Following exchanges with Nottinghamshire police, in October 2016 we directed the force to hold gross misconduct hearings for two officers alleged to have used excessive force.We have reviewed the delays in this case and are implementing improvements to our processes.’’

Wallace’s solicitor, Carolynn Gallwey of Bhatt Murphy Solicitors, said: “What is most shocking about this case is that it was a number of officers, across shifts and including supervising officers, who either actively took part in or didn’t care enough to stop the humiliation, assault and abuse of a heavily pregnant woman.”

In a letter to the IPCC, Gallwey writes: “Ms Wallace is living with a terminal cancer diagnosis, and she is anxious to see this matter resolved in order that she is not forced to leave it to her children to litigate on her behalf after her death.”