As Downton's aristocratic sisters Lady Mary and Lady Edith, you'd imagine Michelle Dockery and Laura Carmichael revelled in the opportunity to sashay around in beautiful gowns all day in the hit period series, but as the sixth and final run begins, the pair reveal they're relieved to be bidding farewell to their characters' glamorous garb.

"It's definitely a fantasy to be on set doing a job without being sewn in for the fifth time in the day," says 29-year-old Carmichael, laughing.

"I think we've all had days where we've been like, 'I can't wait to just be in jeans and a T-shirt with messy hair!'" adds the actress, who grew up in Southampton.

As such, neither was tempted to take one of their costumes home.

"The costumes are ready to go in exhibitions," says Dockery, 33, who grew up in Rush Green.

"The detail and beauty of some of those costumes... the world needs to see them actually. It would seem a waste to just be in my wardrobe, because it's not like I would be swanning around my place doing the washing up in one of Mary's flapper dresses."

Without their characters' finery, Dockery and Carmichael can usually walk around without being recognised.

Still, with an average of 8.4million tuning in during the last series in the UK alone, it's not only sherry sales, the butler trade and the UK tourism industry that have benefited from the 'Downton effect'.

Indeed, there have been brushes with George Clooney - who appeared in the Text Santa special last year - trips to the Golden Globes and Emmys, and famous fans in Beyonce, Sandra Bullock, Ashton Kutcher and Mila Kunis, as well as the Duke and Duchess of Cornwall.

But back in 2010 when Downton started, they were relative unknowns, with Dockery having appeared as Eliza Doolittle in the stage production of Pygmalion and Carmichael barely out of her training at the Bristol Old Vic.

"When we started this, it was ours and it was so special," recalls Dockery. "That first series was just the most amazing thing, and we never would have imagined that all of these people in 250 territories would fall in love with the show.

"To us, it still kind of feels like that - this special thing we experienced in the early days. When we're at work, it's like nothing has changed. It's the stuff that goes on outside of that which is still now baffling."

And nothing much has changed between Lady Mary and Edith's sisterly relationship, which is perhaps at best frosty and at worst hostile.

"We'll see them p**s each other off a bit," explains Carmichael. "They've both created these new lives for themselves, and without their brother-in-law Tom, Mary is running the estate. Edith's living in a house where Mary is queen bee, and Edith's flitting off to London having a brilliant time, which annoys Mary."

And although Carmichael describes herself and Dockery as "two very modern, emotional women", who often ask if their characters "can just have a hug" during tense scenes, they'd rather have a bit of bite to their storylines.

"They're family. They can't escape one another, they always will be family, so it's not something that will end either in a good way or a bad way, it is what it is," reasons Dockery.

"We love it whenever [Downton creator] Julian Fellowes writes something juicy for Edith and Mary, as it's more fun for us to play. We get a bit bored when they're being vaguely nice to each other."

And after Mary's doomed will-they-won't-they romance with Matthew, played by Dan Stevens, as well as a few dalliances with some dashing blue-bloods, it looks like the eldest child of the Crawley clan is going to let her love life take a back seat this series.

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"There's always one or two [suitors] on the go," Dockery admits with a smile. "But with Mary, this year, it feels like she's struggling more with herself, rather than her relationships.

"In the end, what I've always wanted for the character is for her to be content and happy in herself, because she kind of got there with Matthew and then all that tragedy happened. Ever since, she's been trying to rebuild her life and like herself, and that's the thing with her - she just wants to be happy."

While Downton Abbey will be put to bed in the UK by the end of the year, the series will ripple on in the States and across the world, where it is shown later.

And understandably the two actresses are feeling ambivalent and "emotional" about the end, already planning mass meet-ups with the cast and crew.

"It's a very strange feeling, but at the same time, there's lots to celebrate," says Dockery.

And part of that celebration comes from appreciating the opportunities the period drama has given them.

"It's a gift to be at the beginning of our careers with this on our CVs," says Carmichael.

"It has completely transformed things [for us]. But the biggest gift is just to be working with these incredible people.

"It feels a little bit like we're coming out of school, like we're graduating and we've had the best teachers in the business; Hugh [Bonneville] and Jim [Carter] and Maggie [Smith] and Penelope [Wilton] and Phyllis [Logan]... It's just the biggest list of people who've led by amazing example.

"That's the thing that's been invaluable about the whole experience."

Downton Abbey begins on ITV on Sunday, September 20. 

Keeley Bolger