By contrast, the actresses who play the aristocratic Crawley sisters -Michelle Dockery (Lady Mary) and Laura Carmichael (Lady Edith) - wear beautiful costumes in every scene, but often go unrecognised in their off-duty wear. Carmichael said she "can still go to Sainsbury's" without attracting attention because she looks so different in ordinary clothes.
Froggatt described herself as "not a classic beauty", and said she was pleased about that, as it meant she was not pigeonholed in certain roles.
There was one advantage to playing a servant and having such a limited on-set wardrobe, according to Froggatt.
She said: "We barely had to do any costume fittings. We'd get two dresses at the beginning of the series and that would be that for six months of shooting. Whereas Michelle, Laura and the others were going in for hours and hours of costume fittings.
"I could lie down at lunchtime and know I wasn't going to crease my dress because it was made out of modern material, whereas some of the dresses the girls upstairs were wearing were very, very delicate and very expensive, and they had to be extremely careful lying and sitting down."
Froggatt's performance as Anna Bates, who suffered a rape ordeal in series four at the hands of a visiting valet, has already won her a Golden Globe this year and got her an Emmy nomination. It also provoked dozens of complaints from shocked viewers.
The actress had no idea of that storyline until she read the script three weeks before the scenes were to be filmed. Until then, she had worried that the plots for her character were becoming a little dull.
"I felt series three was a bit quiet for me, so I was worried because we'd just signed up for series four and five and I was thinking, 'Hmm, I hope I'm not just going to be saying: 'Here's a tray'," she said.
"I was really shocked. I never in a million years expected it to be that. And then my second reaction was, wow, this is a huge responsibility. I always thought it would be controversial.
How could it not be? But I didn't expect it to be as controversial as it was."
Downton had eight nominations at the Emmys, including outstanding drama series. American audiences have fallen in love with the show, and will be as bereft as British viewers when it comes to an end this Christmas.
Froggatt said she had experienced "an element of grieving" over the demise of the show, but she is busy with Dark Angel, a two-part ITV drama in which she plays Britain's first known serial killer, Mary Ann Cotton.
Lowdown
Who: Joanne Froggatt
What: Downton Abbey, the final season
When: Starts on Prime, October 15, 8.30pm
