One of the few actors to win the treble of an Oscar (two), Emmy (four), and Tony, Smith’s long career started on the stage in the 1950s.

King Charles led the tributes, saying he was deeply saddened by the news of Smith’s death.

“As the curtain comes down on a national treasure, we join all those around the world in remembering with the fondest admiration and affection her many great performances and her warmth and wit that shone through both on and off the stage,” the monarch said in a statement.

Prime Minister Keir Starmer said Smith “introduced us to new worlds with the countless stories she acted over her long career”.

“She was beloved by so many for her great talent, becoming a true national treasure whose work will be cherished for generations to come,” he said.

For many younger fans in the 21st century, she was best known as Professor McGonagall in all seven “Harry Potter” movies, and the Dowager Countess in the hit TV series and movie spin-offs of “Downton Abbey”, a role that seemed tailor-made for an actress known for purse-lipped asides and malicious cracks.

Her first Academy Award nomination was for her turn playing Desdemona opposite Laurence Olivier’s “Othello” in 1965, before winning the Oscar for her role as an Edinburgh schoolmistress in 1969’s “The Prime of Miss Jean Brodie”.

She won her second Oscar for her supporting role in the 1978 comedy “California Suite”, a performance that prompted co-star Michael Caine to say: “Maggie didn’t just steal the film, she committed grand larceny.”

Other critically acclaimed roles included Lady Bracknell in Wilde’s “The Importance of Being Earnest” on the West End stage, a 92-year-old bitterly fighting senility in Edward Albee’s play “Three Tall Women”, and her part in 2001 black comedy movie “Gosford Park”.

In 1990 Smith was knighted by Queen Elizabeth and became a Dame.