A violent moped bandit who mugged four people for their expensive watches in just 20 minutes while riding around central London has been jailed for nine years.

Bradley White, 29, wore a crash helmet to hide his face as he threatened his victims with a knife in the attacks carried out in broad daylight.

One victim, interior designer Michael Weisser, 79, had been warned by the Metropolitan Police’s Flying Squad that his expensive car and £80,000 Richard Mille watch could make him a target. He had taken to wearing a replica watch when White struck.

Another victim, Charlie Rolls, lost his grandfather’s watch to White when he was ambushed from behind and a knife was held to his throat, Blackfriars crown court heard.

White’s offending had been “escalating” since 2011, when he was part of a smash-and-grab gang which stole £1 million of designer goods in a series of raids on West End stores.

He was jailed for that crime spree but carried out another raid on a jewellery store just three months after being released from jail in 2013. The latest offences occurred within a year of a prison release.

Sentencing White to nine years in prison with an extra three years on licence yesterday, Judge John Hillen told him: “You are a dangerous criminal. You targeted your victims for their high-value watches, and caused them terror and physical harm.”

The court heard the robber has admitted “feeling a rush of adrenaline” after the crimes, and he was deemed a risk to the public by the judge.

White carried out the crime spree on March 5, riding a scooter with stolen numberplates and wearing the crash helmet and hi-vis jacket.

He struck first in Sloane Street at 11.30am, brandishing an 8in combat knife at Jack Nounou, 73, who handed over his £1,000 Shinola watch.

Just five minutes later Mr Rolls was robbed in Brook Street, Mayfair, as White shouted at him: “Give me your f***ing watch” and pinned his victim into a corner at knifepoint.

White struck again at 11.45am but failed to snatch a £10,000 Rolex watch when the victim fought back, and he then arrived at Mr Weisser’s shop in George Street, Marylebone.

He was caught later the same day as he tried to sell some of the stolen watches in the street.

White, of no fixed address, pleaded guilty to three robberies, an attempted robbery, and two charges of theft.

He will serve at least six years of the prison sentence, and will then have to convince a parole board he is safe to be released.