Researchers at University College London examined police reports on 6,511 street muggings in North London and 4,200 in and around Glasgow, and found that London muggers were two and a half times more likely to attack after dark.
In Glasgow, they were only 20 percent more likely - which the researchers put down to the cold. It's not necessarily that the muggers are feeble: just that there are fewer people on the streets.
"It is... interesting to note that the effects of darkness were more pronounced in London than in Glasgow," the researchers note in the paper.
"One reason for this might be variation in the comfort of the external conditions: the temperatures can become very cold at times in Glasgow and that it is more likely to rain in this area. Perhaps on occasion, more extreme conditions limit the number of suitable targets and offenders on the street."
Even in London, muggers prefer warmer temperatures: street robberies increased by one percent for every degree Celcius the temperature rose.
First, says the Met, be extra-alert at tube and bus stations, cash machines, car parks and crowded places, and keep a careful eye on your belongings. But don't flash them about: "Displaying expensive jewellery or electronic devices, like mobile phones or cameras, could attract unwanted attention," they say.
Indeed, with phones a particularly common target, the Met advises against using one immediately after leaving the tube, texting while walking, or even leaving your phone on the table in front of you at a restaurant. Showing off flashy jewellery is similarly a no-no.
While the latest figures from the Office for National Statistics show that overall crime has fallen by five percent over the last year, mugging and pickpocketing have risen by eight percent.