Thieves on scooters and pedal cycles are committing up to 50,000 offences a year in an alarming new crimewave, police revealed today.

Gangs of youths are using stolen scooters, mopeds, motorcycles and bikes to commit tens of thousands of snatch offences across London, detectives say.

The full scale of the moped crime surge came as police revealed details of an alarming new tactic in which a gang sprayed a fire extinguisher into the face of a motorcyclist in a bid to hijack his machine.

Dramatic images caught on the 58-year-old victim’s helmet camera show how he was surrounded by seven suspects on four mopeds and forced to stop in a road in east London.

One of the suspects riding pillion sprays the foam extinguisher directly into his face and the camera shows him falling to the floor.

The group were unsuccessful and fled the scene.

Today detectives appealed for information on the gang who are wanted in connection with a total of seven offences in the Barking and Dagenham area in just two days last month.

The appeal came as senior officers from Operation Venice, the Met’s campaign against moped crimes, told the Standard how they were combating the explosion in “two wheeled” crime across the capital.

They revealed how gangs of mainly teenage boys are stealing mopeds in outer London borughs and using them to commit snatches in the West End - often motivated by the thrill of speed.

Detectives say they are targeting at least 500 known offenders behind the crime spree - with suspects moving between using stolen mopeds and pedal cycles to snatch mobile phones.

Police also urged Londoners to take simple steps to help prevent crimes, in particular warning scooter owners to use locks to secure their bikes in the street.

The scale of the offending can be revealed in new figures released by the Met which show thieves are stealing around 1,500 scooters or motorcycles in London every month.

In addition, the same criminals are using scooters or pedal cycles to commit 2,500 theft offences a month, most of them mobile phone snatches.

Thefts involving mopeds or motorcycles are currently running at 13,005 over the past 12 months, a 41 per cent increase over the previous period.

Commander Julian Bennett, who is in charge of Operation Venice, said: “This is coming up to 50,000 crimes a year so this is a significant issue.

Advice from police Scooter riders: lock more than just the front wheel. Lock to secure street furniture. Cover the bike to deter thieves. Mobile phone users: don’t come out of Tubes and look at your phone, use a hands free, be aware of who is around. Record IMEI number.

"This is a serious crime because of the risk to everyone involved, including the riders, pedestrians and the victims of the snatch. This is completely unacceptable.”

Police say moped crimes, once mainly confined to boroughs such as Islington, Hackney and Haringey, are now spreading across the city and beyond.

Earlier this week a covert police team seized a suspect in Islington who had travelled to London from the Thames Valley area.

Officers say part of the problem is the ease in which gangs can steal scooters by simply breaking their steering locks.

They point out there are more commuters using inexpensive scooters to avoid expensive rail fares but most don’t leave their machines securely locked.

Superintendent Mark Payne, who is co-ordinating the Met’s prevention campaign, said: “They take the key out and think it is OK to walk away from but the average thief can steal a scooter in 30-40 seconds.

"If people take more care and use locks to secure their machines there will not be as many stolen scooters around so there will be less crime."

Police admit difficulties in securing evidence against the gangs who hide their faces while the Met’s pursuit policy means officers have to adhere to strict guidelines before chasing a scooter or motorcycle rider at high speeds through London.

However, police insist they still carry out pursuits - earlier this week a teenager was arrested in Penge after a chase involving the police helicopter and a stinger device used to puncture his tyres.

In a series of new measures designed to tackle the moped gangs the Met announced:

A revamped Operation Venice campaign to co-ordinate action across London’s 32 boroughs

Extra covert patrols to catch the bike thieves red-handed and plans for “tougher tactics” to seize offenders in the act.

More sophisticated forensic techniques to track criminals to avoid the risk of a chase.

A specialist tactical traffic advisor who can authorise high speed pursuits on duty 24/7 in the Met’s central London control room.

A new facility to capture footage of scooter crimes taken by members of the public.

Special ‘recognisers’ being used to spot known offenders - one suspect in a recent spree of incidents outside the BBC was recognised by a mole on his forehead.

Police refuse to give details of the tougher tactics but say it will allow officers to intervene more effectively and safely if they encounter scooter thieves.

Supt Payne said suspects occasionally took off helmets in a bid to force police to abandon chases but he said: “If a rider takes his helmet off, that’s a result for us. They will drive past five or six CCTV cameras and we will have his face.

“We know who they are and there is no point in pursuing them. We will bang on their door at 3am when it is low risk, why should we bother chasing them through the streets of London.”

Restrictions on pursuits were enforced more strictly after the death of 18-year-old Henry Hicks who was killed when his moped crashed as he was being chased by police December 2014.

Four police officers are facing misconduct charges after an inquest jury rejected their account that Hicks was not aware he was being followed.

Detectives say they are gathering intelligence on around 500 suspects committing scooter or cycle crime across London but believe more are involved.

A team focuses on a dozen top offenders at a time, targeting them with proactive patrols, bail and curfew checks and working with the local authority on diversion.

Detective Superintendent Stuart Ryan, who is in charge of operations against the gangs, said most offenders were in their teens and early 20s and some were organised in groups of around five to 10 people who use a stolen bike for a period before dumping it.

The bikes are stolen in outlying boroughs and used to travel into the West End to commit crimes.

Many prolific offenders have 20 or so crimes to their name, one 15-year-old was only jailed after being arrested 80 times.

He admitted police often played “wack-a-mole” with gangs who appear at different times and locations across London.

He said “They can change their tactics every single day. You can see mopeds driving around just to see what the crowds are like and whether police are around. “Some of the groups do seem to talk to each other, to warn if the police are around. They are professional at this.”

Some offenders were diverted but there was a hard core who were more difficult to reach.

The offenders come from a mix of backgrounds, some of them wealthy, who are driven by a desire for kicks.

Det Supt Ryan said: “Part of it is about speed, they need a thrill. Some of it is money but their network is based on their social and geographical network.

“They enjoy it because the feedback we have had from them is they enjoy the speed, they enjoy going fast and they enjoy the easy money, it is better money than McDonald’s and their friends are doing it.”

The crimewave is being driven by a new demand for spare parts in mobile phones with iPhone screens costing as much as £150 to replace.

Each stolen iPhone can fetch £100 and there are cases of thieves snatching 20 or more in the space of an hour in central London.

Thefts of mobiles fell dramatically three years ago when new security was brought in but the second hand market for spare parts and re-sale value of iPhones caught police by surprise.

Detectives have discovered thieves can spot what sort of phone you are carrying either in your pocket or from a few hundred yards away.

Police know because they asked suspects in custody to identify different phones in people’s pockets, they knew what phones they had just from the size of it.

Police also have evidence the gangs practise on each other on estates to become better at snatching phones from pedestrians in the street.