Hundreds of British soldiers have received letters questioning their role in claims of torture and murder during the Iraq War.

Around 280 veterans have been sent documents telling them they were involved in an incident under investigation by the UK's government-established Iraq Historical Allegations Team (IHAT).

More than 50 deaths during the UK's military mission in the country between 2003 and 2009 are set to be investigated, prosecutors have confirmed.

Unlawful death cases involving 35 alleged killings have already been referred to the Service Prosecuting Authority (SPA) - the military equivalent of the Crown Prosecution Service - along with 36 cases of alleged abuse and mistreatment.

The SPA is also preparing to advise on an additional 20 cases of unlawful killing and 71 cases of mistreatment in the near future.

Andrew Cayley QC, the director of the SPA, said it "will not flinch" in prosecuting British soldiers where there is evidence of wrongdoing.

He said: "I have spent the last 20 years of my professional life advising and prosecuting in cases involving genocide, crimes against humanity and war crimes.

"I know very well what these crimes look like.

"Make no mistake we will give all these IHAT cases the thorough scrutiny the law requires and if prosecution is warranted we will not flinch from proceeding.

"Equally I want to make it absolutely clear that no member of the British Armed Forces will be prosecuted unless there is sufficient evidence to do so."

British forces withdrew from Iraq in 2009 although lawyers are continuing to refer cases to IHAT.

The multimillion-pound inquiry's workload reached 1,515 possible victims by September, of whom 280 are alleged to have been unlawfully killed. 

An IHAT spokeswoman confirmed some of the letters sent to veterans had been hand delivered by detectives and that there was "no obligation to respond".

She said: "It is standard police practice to send letters as a means of contacting potential witnesses.

"Sometimes the letters are delivered by hand and it may be that if a potential witness is at home then the investigator will take the opportunity to ask a few questions."

A British defence ministry spokeswoman said: "The vast majority of UK service personnel deployed on military operations conduct themselves professionally and in accordance with the law.

"The MoD takes all allegations of abuse or unlawful killing extremely seriously. That is why we are ensuring that they are investigated to establish the facts."