One of London’s most prolific moped gangs responsible for an extraordinary crimewave of 103 offences in 18 days has been smashed by police.

The teenage offenders – aged 15, 16 and 17 – grabbed phones from pedestrians in Westminster, Camden, Islington, and Kensington and Chelsea during their crime spree.

In one horrifying incident, captured on film by an Evening Standard photographer, the boys took part in a raid in which two moped riders carrying pillion passengers mounted the pavement outside the BBC’s headquarters near Oxford Circus.

One was wielding a hammer and another used a crowbar to intimidate terrified passers-by as they rode at high speed along footpaths to snatch phones from their owners.

The trio, who are all from Islington, are now in custody awaiting sentence, however, after being arrested by police and confessing to their crimes at Southwark Crown Court.

Two of the boys also admitted breaching criminal behaviour orders banning them from riding mopeds because of previous offending on scooters.

The scale of offending by the trio, who pleaded guilty to conspiracy to commit robbery, was so extensive that the number of “moped-enabled” crimes in the capital is said by police to have fallen significantly since their detention.

Their conviction follows mounting concern about moped crime in the capital. In many cases, offenders have ridden stolen mopeds along busy pavements, putting pedestrians in danger, to grab phones from their owners.

In the incident outside the BBC, at least one woman had her iPhone snatched as the criminals rode at high speed threatening pedestrians with their weapons.

In a further case this year, a man suffered a broken leg after being run down by moped thieves as he walked outside a Park Lane hotel. Another rider drove onto the pavement outside Selfridges in Oxford Street on a Vespa to snatch two mobile phones.

Scotland Yard said that it was unable to comment in detail about the conviction of the three teenagers ahead of their sentencing, which is due later this year, for legal reasons.

But it confirmed the successful prosecution, saying: “ Three youths have pleaded guilty to conspiracy to rob following a spate of moped-enabled robberies in central London. The charge relates to 103 separate offences committed in central London between 18 April and 5 May.”

A spokesman added that most of the crimes had been carried out within one square mile covering Westminster and Camden. Other offences also took place in Islington and Kensington and Chelsea.

The successful prosecution of the teenagers follows a crimewave involving offenders on mopeds carrying out robberies and snatches. Met figures show moped-enabled crime has risen seven-fold in two years, from 1,053 in 2014 to 7,668 last year.

Police have drawn up a list of about 200 individuals who they suspect of the majority of moped-related crimes.

Many have proved hard to prosecute because of the difficulty in securing evidence so the conviction of three of the most prolific criminals is viewed as a significant success.