Thugs leave a man, 50, fighting for his life after beating him unconscious outside the National Gallery

Shocking CCTV footage captured the moment a thug floored a man with a single punch from behind as he walked through London's Trafalgar Square.
Seconds after crashing to the floor, the victim is violently kicked by another man as he lies motionless.
Having carried out their cowardly attack outside the National Gallery, the two men are seen calmly walking away from the scene.
The 50-year-old victim suffered serious injuries in the assault, Metropolitan Police said, and he remains in a critical but stable condition in hospital.
Detectives from Westminster's Serious Crime Unit are investigating the attack, which occurred outside the National Gallery at about 0.40am on June 3.
Metropolitan Police have now released the footage in a bid to identify the two men or to trace witnesses, with no arrests made in the investigation.
The first suspect has a top knot hairstyle, full beard, red t-shirt, dark trousers and light-coloured shoes.
The second suspect was wearing a black jacket with a white emblem on right shoulder and white writing with a picture on the rear.
He was also wearing a white top under the jacket, dark trousers and dark shoes with white soles.
Anyone with information is asked to contact Westminster Serious Crime Unit on 07500 766462; you can also tweet information via @MetCC.