Keira Knightley will eat "something disgusting" to give herself bad breath if she has to kiss co-star she "hates"

During an appearance on the Dish by Waitrose podcast, she explained: "Oh yeah, yeah, yeah, there's etiquette.

"If you really hate somebody obviously then you have something disgusting and like you smell. But if you really someone obviously there's chewing gum, you need to be minty fresh.

"No, that's unspoken basic human [etiquette] ... like you're not having garlic for lunch, you know, once again unless you really hate them in which case as much garlic as possible, obviously that's fair enough. "

Keira stars in the new Waitrose Christmas advert alongside comedian Joe Wilkinson and she insisted they both had fresh breath for the kissing scene.

She said: "Tongue? No tongue. I mean, there was no tongue! I mean the rule is no tongue. Yeah, that is the rule. Waitrose Xmas no tongue. No tongue. Fine ...

"We were both minty fresh ... He was so sweet. He's got such a large beard that I couldn't get close to his mouth ... I don't think I got beyond the beard. It is a thick beard. An amazing beard."

When asked if Joe was nervous about the smooch, Keira replied: "I mean it is weird, especially when you've only met somebody like two minutes before and then you're suddenly like ... yeah, it's quite weird.

"Although I don't remember him being that [nervous] ... I think he was fine with that, it was more like, it was the dancing, he was not fine with the dancing, and then he really went for it and was great. You know but I feel like he was fine."

The advert spoofs Keira's rom-com Love Actually as a romance plays out between Phil (played by Joe) and Keira, who appears as herself, and ends with Phil presenting Keira with a pie at her front door and the actress saying: "Please say you don't have cur cards" in reference to a famous scene in her 2003 film.