Dame Maggie Smith has said her work in the Harry Potter films and on Downton Abbey “wasn’t what you’d call satisfying”.

The actor, 84, played schoolmistress Minerva McGonagall in the boy-wizard films and the waspish Violet Crawley in the period drama. Discussing the earlier years of her career, she told ES magazine: “It seemed to take ages to get away from light comedy.”

She added: “I am deeply grateful for the work in Potter and indeed Downton, but it wasn’t what you’d call satisfying. I didn’t really feel I was acting in those things.”

Smith returned to the stage this year as Joseph Goebbels’ secretary in the Christopher Hampton one-woman play A German Life. She said that as soon as she agreed to do it, she suffered “doubt, doubt, doubt”.

“I suddenly felt twice as old as I actually was,” she said. “And also, when you haven’t done a show for a long time, there’s something pretty dumb about doing it totally on your own.”

The long-awaited Downton Abbey movie made almost $200m on release earlier this year, with home entertainment numbers expected to be healthy. Smith was reported to be on of the last cast members to agree to the feature film; her involvement would also be key to any sequel.

Speaking about the possibility of a followup last week, one of the film’s producers, Graham Neame, confirmed there is a potential film in the works.

“We’re working on what the story is,” he said, “and when we might be able to make it.

“But it’s the same as the first time around: we have to try and get everyone back together again. And that was very challenging.”