Jon Hamm's 'Mad Men' co-stars turned "yellow and sallow" after attempting to smoke real cigarettes on screen

Speaking at the ATX TV Festival in Austin, Texas, at the weekend, he said: "I think somebody did a count, and in the pilot alone, I smoke 75 cigarettes.

"They are fake cigarettes, but that just means that there's no nicotine in them. It doesn't mean you're not burning something."

Of his castmates, he added: "They were like, 'We're gonna smoke real cigarettes. We really want to, feel it and do it.'

"And I was like, 'Let me know how that goes.' And within three days, they were yellow and sallow. This is a terrible idea."

And because 'Mad Men' was set in New York but shot in Los Angeles, most of the filming took place indoors, making the smoky situation even trickier to deal with.

Jon said: "We didn't go outside, which was awesome and not awesome. The whole thing, the whole stage is full of fake cigarette smoke."

And to replicate a vodka martini, 'Mad Men' bosses added onions to water.

Jon quipped: "Oh, the breath was lovely."

His co-star John Slattery, who played Roger Stirling, laughed: "Pop another pearl onion in your glass of water, and then smoke 26 more fake cigarettes and it's 9:30 in the morning!"

The two stars also recalled how the first day of shooting 'Mad Men' was interrupted by the discovery of a dead body in the parking lot.

Jon said: "Scene one, day one, there was a dead body in the parking lot, but that's a story for another day."

John added: "That's true. First day of work, a guy fell off a bridge, and he was in the parking lot, face down. I saw a foot."

In 2015, AMC, who broadcast 'Mad Men', released some statistics to mark the programme's finale, which included the revelations that the characters had smoked a staggering 942 cigarettes and poured 369 drinks between them across all seven seasons.