Former United Lincolnshire Hospitals Trust chief executive Gary Walker has accused Sir David Nicholson and senior NHS leaders of putting targets ahead of patient safety.

Mr Walker today said he had breached the terms of his £500,000 confidentiality agreement with the trust to speak to the media about his case.

He claimed he had written directly to Sir David, the NHS chief executive, and the then East Midlands Strategic Health Authority chief executive Dame Barbara Hakin.

Mr Walker was sacked in 2010 for gross misconduct for allegedly swearing during board meetings. He today said his trust board decided to abandon waiting time targets because of soaring emergency demand in 2008 and 2009.

Ahead of an employment tribunal in October 2011 Mr Walker signed a settlement deal preventing him from speaking about the issues.

He claims a centrally driven “bullying” and “target” culture had led to unnecessary deaths at the trust since his departure three years ago. He first raised concerns in 2009.

United Lincolnshire Hospitals was last week named as one of 14 trusts with high mortality rates being investigated by NHS medical director Sir Bruce Keogh, in the wake of last week’s Francis report into the failure at the Mid Staffordshire Foundation Trust.

Mr Walker told BBC Radio 4’s Today programme he was ordered by East Midlands SHA to hit the targets “whatever the demand”.

Mr Walker, who joined the United Lincolnshire Trust in 2006, said in a statement to media: “By April 2009 demand [at the trust] was out of control and fearing patients were coming to harm, I explained to Barbara Hakin that I was going to get an external review into mortality. I was told to resign or my 20-year NHS career would be in tatters.

“A culture exists in the NHS driven from the centre that makes it hard for chief executives and senior leaders of the board to keep their jobs without endangering patients. They are not encouraged to speak out – in fact they are actively discouraged to do so. This is dangerous, very dangerous.”

The SHA, responding in a statement, said “it totally refuted” Mr Walker’s claims and had always acted in the “interests of patients”.

Ahead of the BBC interview Mr Walker received a letter from solicitors acting for United Lincolnshire Hospitals warning the trust would be entitled to seek the return of payments made to him and any legal costs.

A spokesman for the Department of Health said: “Allegations made by Mr Walker regarding behaviour at the SHA have been independently investigated and found to be without merit.

“It is important to stress allegations of this nature are taken extremely seriously. Following Mr Walker’s initial concerns raised in 2009, Sir David commissioned a rigorous independent review, following which it was concluded that no evidence whatsoever was found of bullying and harassment by the trust or SHA.”

As revealed by HSJ in September, Dame Barbara is currently under investigation by the General Medical Council in relation to her role in relation to United Lincolnshire Hospitals.