Pc Yvonne Fletcher “had her whole career and her whole life ahead of her”, Met Commissioner Sir Mark Rowley has said in a statement paying tribute to the former officer who was shot dead 40 years ago.

On April 17 1984, Pc Fletcher was murdered outside the Libyan People’s Bureau in St James’s Square, central London. She had been policing a small demonstration outside the embassy.

On the 40th anniversary of her murder, Sir Mark said Pc Fletcher was “just 25 when she was callously murdered” and was “simply doing her job, policing protest, not unlike what many officers do so often today”.

He added: “She had her whole career and her whole life ahead of her.

“Today, 40 years on from that terrible day, I join with all in the Met and across policing in paying tribute to her, in recognising her sacrifice and in keeping her family, friends and colleagues in our thoughts.”

A man was arrested on suspicion of conspiracy to murder Pc Fletcher in 2015.

However, for national security reasons, much of the evidence against him could not be used in court and the Met was unable to charge him.

Pc Fletcher’s family said they would like to thank the Met for its continued support in a statement released on their behalf.

They said: “It was 40 years ago today that Yvonne was just doing her job policing another demonstration when she was tragically killed in St James’s Square.

“Over the years Yvonne has always been in our thoughts along with all those affected on that fateful day.

“As in previous years the family has chosen to spend the day privately reflecting on the sister we knew and loved without any media intrusion.”

Police said the family did not plan to make any further statements as they marked the anniversary.

There are currently no active lines of inquiry and the likelihood of finding further evidence remains low, the Met said.

However, the force said the murder investigation will never be closed and any relevant new information that comes to light will be assessed and investigated further as appropriate.