On Monday evening, the highly-anticipated film was debuted and ahead of the screening, the cast posed for pictures outside Cineworld Leicester Square.
Set in 1927, the film, created by Julian Fellowes, picks up the action two years after the 2015 Christmas special, which was set in 1925.
It will see the occupants of Downton Abbey, both above and below stairs, buzzing when it is announced that the King and Queen of England are to pay a visit.
Also attending the glamourous event were cast newcomers Tuppence Middleton, Stephen Campbell-Moore and Imelda Staunton, alongside Lord Fellowes and the film’s director, Michael Engler.
Dame Maggie, Dockery and Bonneville, who are all reprising thier roles, were also present alongside Allen Leech, Dame Penelope Wilton, Joanne Froggatt, Phyllis Logan, Elizabeth McGovern, Jim Carter, Laura Carmichael and Lesley Nicol.
Leech arrived with his wife Jessica who revealed her pregnancy at the event. The pair walked down the aisle in a romantic ceremony in Santa Barbara, California in January 2019.
Michelle Dockery, who plays Lady Mary, said: “It felt like we had never left, there was this real buzz because we were making a movie.
“It feels like such a privilege. We did the show for so long and now filming a movie, there was a lot of excitement, like we had never been away.”
She added: “In those first 20 minutes we were like ‘We are doing a film! Our faces are going to be much bigger!’ but we mustn’t treat it any different.
“It is an extension of the show, but turned up a notch, it was important that it didn’t feel too different.”
Laura Carmichael, who returns as Lady Edith, added: “I had the initial nerves of being back and it’s a movie, how is that different?
“But that lasts about 20 mins and we relaxed again, it feels like coming home, as cheesy as it sounds, it did feel like that.”
Lesley Nicol, who plays cook Mrs Patmore, addressed new stars joining the cast, saying: “The people who came in said they felt relaxed and welcome which is what we try to do because it’s hard and when it’s a big deal it’s even worse.
“We greatly admired what all of them did.”
Actor Kevin Doyle has said he modelled an absurd curtsy he performs in the Downton Abbey film on former prime minster Theresa May.
Downton Abbey: Official movie trailer released
The actor, who plays footman Joseph Molesley in the TV series and in the new big screen version, told a press conference: “I modelled the bow/curtsey on Theresa May.
“She was meeting some royal or another and it was such a preposterous curtsy I thought ‘I’m going to have that’”
Downton Abbey is released in UK cinemas on September 13.
Additional reporting from Press Association.