The Metropolitan Police has announced the launch of a murder investigation after a man beaten by thugs in a “mindless” attack in Trafalgar Square died in hospital.

Desmond O’Beirne died from head injuries on December 20, more than six months after the brutal attack in the early hours of June 3rd last year when he was punched and kicked outside the National Gallery.

Murder detectives at Scotland Yard are appealing for witnesses and information to catch Mr O’Beirne’s killer, having previously released CCTV footage of the attack in which one man can be seen chasing the 51-year-old and punching him in the back of his head.

As the victim collapses onto the pavement following the deadly blow — from which he never regained consciousness — the clip shows a second man run up to kick Mr O’Beirne, before both assailants walk casually away from the scene.

Shot just after midnight, the footage appears to have been brightened digitally. Police have described the first suspect as having styled his hair in a “top knot”, while they say the second man was wearing a black jacket with a white emblem on the right shoulder, and white writing with a picture on the rear.

London Mayor Flips on ‘Stop and Search’ After Breitbart Exposé of Capital Crime Epidemic https://t.co/fLsM8XvF51 — Raheem Kassam (@RaheemKassam) January 11, 2018

DCI Noel McHugh said: “These two men will have spoken to friends and partners and possibly boasted about their mindless attack. I want you to call us with their names.

“The males are distinctive and will be known to their group that evening. Desmond never regained consciousness after the brutal attack and it is vital we bring his attackers to justice.”

While the election in 2016 of London’s first Muslim mayor Sadiq Khan was lauded by the media both in Britain and internationally in 2016, the city has since become increasingly violent, with the Labour politician presiding over huge jumps in knife crime, gun crime, acid attacks, rapes, and other types of crime — including youth homicide, which shot up 70 per cent in just one year.

During his term so far, the mayor has lashed out with increasing frequency at Donald J. Trump, repeatedly calling for the U.S. president to be banned from Britain.

The mayor was forced to suspend a speech to the Fabian Society conference on Saturday morning after pro-Trump and pro-Brexit protesters emerged from the audience in London with U.S. flags, and called for Khan’s arrest.