Sir Bernard Hogan-Howe says that drug-testing would help cut the number of users - as the risk of losing your job would act as a deterrent.
"It seems to me we have got to plant in people’s minds something to affect the demand as well as supply. You can think of many occupations where if you were working with a colleague you would want to be sure in fact that they were drug free."
More top news
The 24-year-old was unarmed and the incident is not being treated as terror-related.
Some platforms have been taken out of service with disruption expected to continue until the end of the day.
The Met Office has extended its weather warnings for snow and ice to cover vast swathes of the country, including London and the South East.