Emily Mortimer on celebration of female friendship in new film Good Posture

“I would love one per cent of that character’s frostiness,” quips 47-year-old Mortimer, who is perhaps best known for HBO series, The Newsroom.

“You need it for life, and I don’t have it, at all; I’m always trying to just ingratiate myself to people and make them like me.”

Of course, playing someone so different to herself wasn’t the only great thing about the film, which is set in current day Brooklyn, and follows the story of Lilian, a young woman who is placed into the care of family friend Julia after a break-up.

There was also the fact it was written and directed by Mortimer’s best friend, Dolly Wells.

The pair, who were born four days apart, have known each other since childhood. Together they wrote and starred in Doll & Em, a Sky Atlantic comedy about two actors called – you guessed it – Doll and Em, who are best friends (it ran for two series from 2014).

Because of how close they are, the filming process for Good Posture, which was “really low budget”, they had just 10 to 12 days to shoot, felt “very free, very collaborative”, recalls Mortimer.

“Dolly’s so un-authoritative, but had a really calm, quiet confidence, that I didn’t expect,” she says.

“I mean, I didn’t know what to expect, but then I suddenly saw her in this role, and she was amazing.

“In the centre of all this chaos and confusion, she was just able to breathe and not be panicking.”

She adds affectionately: “I think the atmosphere that Dolly created on this set was a very rare thing – and the best directors I have worked with have created that atmosphere – where you feel ‘seen’.

“There’s a sort of feeling, despite all of it, that there’s all the time in the world to be you at that moment, and they’re right there with you and they believe in you.”

Both Lilian and Julia are fascinating, watchable characters. At the start of the feature, they have a passive-aggressive relationship, amusingly portrayed through notes they write to each other.

After Lilian suddenly decides to make a – admittedly unauthorised – documentary on Julia, to impress her ex-boyfriend and others, a rather surprising inter-generational friendship starts to develop.

Discussing the story, Mortimer reveals there were definitely elements of Julia that she could relate to – particularly the idea that both she, and Lilian, have always been defined by men.

“I think Dolly was making a really interesting point with that; you spend your life seeking the approval of men, and then you suddenly realise that actually you could get a quite exciting and fulfilling relationship from being friends with another woman, and that that might be more interesting, actually.