• Firearms officer used song titles in inquest evidence • Marksman may have fired shot that killed Mark Saunders • Songs included Enough is Enough and Point of No Return

A Metropolitan police firearms officer who may have fired the shot that killed barrister Mark Saunders has been removed from firearms duty after allegedly inserting song titles into his oral evidence at the dead man's inquest.

The Independent Police Complaints Commission said it is investigating the unnamed officer, who gave evidence as Alpha Zulu 8 or AZ8, after it emerged that he had been reprimanded by his superior shortly after giving evidence on 27 September.

Saunders was shot dead by firearms officers in May 2008, following a five-hour armed standoff at his flat in Chelsea, west London. Last month a jury at Westminster crown court ruled that the barrister, who was an alcoholic and armed with a 12-bore shotgun during the siege, had been killed lawfully.

The inquest heard that AZ8, who was stationed on an adjoining conservatory rooftop was one of two officers who may have fired the fatal shot.

An examination of the transcript shows that evidence given by AZ8 contained a number of phrases which are also the titles of songs, including Enough is Enough by Donna Summer, Point of No Return by Buzzcocks, Line of Fire by Journey, Quiet Moments by Chris de Burgh, Kicking Myself by As Tall As Lions and Fuck My Old Boots by the Membranes.

Sources close to the Metropolitan police commissioner, Sir Paul Stephenson, said he was "furious" that anyone could show such "insensitivity and lack of judgment" during the high-profile hearing.

The force confirmed that it had referred the matter to the IPCC last week when the reprimand came to the attention of more senior officers, who judged the sanction to be "insufficient".

"We have now been informed by the IPCC that they will manage an investigation by the Metropolitan police Directorate of Professional Standards," said a spokesman.

He would not confirm which songs are thought to have been inserted into evidence.

But a transcript shows that the officer told the inquest that the shooting was not like in films, where "it's the bad guy who pulls the trigger and the good guy always gets there first". The situation had got "past the point of no return", he said.

"As I play it back in my mind, which is not something I do all the time, but in quiet moments I think about and I feel: 'is there any other way?'. But every time I play it back in my mind it's the same outcome – unfortunately Mr Saunders gets shot because of his actions.

"I switched the light on, he turned towards me and I thought: 'Fuck my old boots, I've got a gun trained on me ...

"As he brings the gun down his finger could be on the trigger. Action will always beat reactions. We have to decide where that point is, and for me as he was bringing it down I thought, 'No. Enough is enough.'"

He told the court: "I would be buggered if I was going to turn my back on a guy with a shotgun. I've got people protecting me, or I'm supposed to, but there's nothing like protecting yourself – self-preservation."

Saunders' mother Rosemary said: "If it's all such a game, was it a game on 6 May? If this man can approach the inquest with such an attitude, then it makes you wonder about how he approaches shooting his gun to kill a man." Mark Saunders' widow Elizabeth declined to comment.

The Met spokesman said the force "takes this matter extremely seriously as we expect the highest standards of all of our staff. The officer has been removed from operational firearms duty".

In a statement the IPCC said its investigation would examine "the officer's testimony, any impact that testimony may have had on the proceedings, the way in which the allegation was initially dealt with by one of his supervisors and whether or not any other police officers were involved".