If you spot someone wandering the Underground in their knickers on Sunday 7 January, don’t panic. They’re not living their worst nightmare: it’s deliberate.

They will be one of more than 100 Londoners partaking in the annual No Trousers Tube Ride.

The tradition began in 2002 as New York’s No Pants Subway Ride. Run by a group called Improv Everywhere, it consisted of just 7 people. 

Now the latest event from the British equivalent has already garnered much attention on Facebook with over 120 ‘going’ and 555 marked as ‘interested.’

Ivan Markovic, the London event organiser, told HuffPost UK that fun seemed reason enough to start the annual event. And it seems to be infectious.

“Over the years we have had other people cheer, ask for photographs and sometimes even join in on the day (on my troop at any rate),” said Markovic.

Although fun, the event does not occur without precautions being made.

(You can’t have fun without rules, people).

The Facebook group Stiff Upper Lip Society (on which the event is hosted) stipulates that attendees not dress in a way that might offend (eg. wearing thongs or banana hammocks). Nor is full nudity or flashing of any kind allowed.

But thankfully the rules are fairly straight forward.

“All we prefer is for any riders not to face any unpleasantness,” continued Markovic. “Not that we have had any over the eight previous rides through London.”

Another strong stipulation is that a) “you’re willing to take your trousers off on the Tube” – so don’t chicken out at the last minute, and b) “you’re able to keep a straight face about it.”

The No Trousers Tube Ride will take place at 3pm on 7 January 2018, kicking off at 11 Newport Pl, Westminster, London WC2H 7JR. While this is open to the public, please heed the organisers’ friendly warning:

This is a participatory event. Do not show up unless you plan to take your trousers off.