A former colleague of policewoman Yvonne Fletcher who was fatally shot outside the Libyan embassy 37 years ago hopes a High Court action over her unsolved killing will bring the justice she “deserves”.

Pc Fletcher, 25, was shot while policing a demonstration against Colonel Muammar Gaddafi outside the Libyan People’s Bureau in St James’s Square in central London on April 17 1984.

Retired police officer John Murray, 66, is bringing a civil claim for a nominal amount of £1 against Saleh Ibrahim Mabrouk, a former aide to the ex-Libyan leader, in a bid to air the “full evidence” surrounding his friend’s death.

Mr Murray’s lawyers had previously hoped to get key material that has been kept secret for national security reasons presented in court for the first time.

Speaking ahead of a three-day hearing at the Royal Courts of Justice in London, starting on Wednesday, Mr Murray claimed that if he won his case it could result in the Crown Prosecution Service reviewing a decision not to proceed with a criminal prosecution.

“I think that once the full evidence is heard in open court and is made public I think a lot of people will be surprised,” he said.

“Everybody knows about the murder of Yvonne Fletcher, what people don’t know, and probably don’t understand is what went on beforehand and what has gone on afterwards, and therein lies a real story.”

Mabrouk, who denies wrongdoing, was arrested in 2015 in connection with Pc Fletcher’s death but two years later the Metropolitan Police said that, while detectives could identify those responsible, charges could not be brought.

This was because crucial evidence had been kept secret to protect national security.

Mabrouk was allegedly inside the Libyan embassy on April 17 1984 when a gunman opened fire from inside the building as both anti- and pro-Gaddafi demonstrators gathered outside.

Mr Murray, from Chingford, east London, who has suffered from Post Traumatic Stress Disorder (PTSD), cradled his colleague as she lay dying, promising that he would find her killers.

“I can recall the events of that day by the minute. It’s still fresh in my mind. I think about it all the time.” he said.

“I was with her in the ambulance on the way to hospital.

“She was still conscious, she was still alive,” he explained, adding that it was then he had “promised” to find out who had “done something to her” and why.

Mr Murray, who is due to give evidence at the hearing this week, said: “It’s taken a lot of time and a lot of money to get here.

“It’s something we shouldn’t have had to do because I do think criminal charges should have be brought.

“What I fought for for all this time is for the full evidence to be heard in front of a judge, and let the judge decide.

“That’s all we want, we want justice at the end of the day.

“That’s what she and all her supporters deserves.”