Offences involving scooters and mopeds have rocketed in London, but the epidemic is yet to spread to the rest of the UK.
In one incident on a Friday night, earlier this month, a heavily pregnant woman became a victim of moped criminals.
In a terrifying attack that took only a few seconds, the 31-year-old mother-to-be was knocked to the ground after thieves mounted the pavement from behind her to snatch a mobile phone out of her hand.
I witnessed the aftermath of the attack in north London from an open window of a restaurant a few yards away. I heard the woman's scream and saw her on the floor, but by the time I'd dialled 999 the two robbers had sped off.
The incident, in East Finchley, a relatively low-crime area towards the southern end of the London borough of Barnet, provided further evidence of the spread of the "moped" crime wave.
(The Metropolitan Police refer to the "step-through-frame" motorcycles commonly used as scooters - mopeds are strictly speaking a subset of scooters, with an engine capacity of less than 50cc).
There are two parts to the crime wave - the theft of the scooters themselves and the offences for which they are used.
The Met says that between July 2016 and June 2017 there were 14,943 thefts of "powered two-wheel vehicles", the vast majority of which were scooters.
The total represents more than 50% of all vehicles stolen in London and is up almost 30% on the previous year.
The calendar year figures show the number of thefts has almost doubled since 2013, though the proportion recovered has increased as well.
It also appears to be a problem largely confined to the capital.
Police in Merseyside and Greater Manchester have set up special teams to combat the illegal use of off-road, or scrambler, bikes, particularly in relation to anti-social behaviour, but none of the major forces we spoke to across Britain flagged scooter theft as a concern on the scale seen in London.
According to the Motorcycle Industry Association, about 60% of all recorded bike thefts in the UK were in London last year, yet just under 10% of all motorcycles and mopeds licensed in the UK were registered to those living in the city.
The number of such offences recorded by police in London has more than trebled in a year.
In the 12 months to the end of June, the Metropolitan Police logged 16,158 crimes involving powered-two-wheel vehicles compared with 5,145 the year before.
Most of the offences were robbery and theft, with mobile phones making up 90% of items stolen. Phones can be reset within minutes and sold on, or used by gang members who like to have a handful of devices each.