Tell anyone under the age of 21 that you were once able to smoke on a planes and their reaction is likely to be one of utter disbelief.

You aren't even allow to smoke in some parks these days, so why did they once let you spark up in an air-tight, flying carriage, they might wonder.

And they’d be right. It seems crazy that passengers could once buy cigarettes from the cabin crew then light them at 35,000 feet without a care in the world. Second-hand smoke? Don't know what you're on about, guv.

However, no matter how ridiculous in-flight smoking may seem today (all planes were smoke-free by the end of end of the Nineties), there remains on aircraft around the world a constant – and mandatory – reminder of those hazy days: the ashtray. Why?!

According to the Federal Aviation Administration's (FAA) list of “minimum equipment” for aircraft, an ashtray in the plane toilet is still a legal requirement.