According to co-star Richard E. Grant, the actress, who will play the lead role of Margaret Thatcher in the upcoming biopic, bursts into song during scenes in reference to her role in Mamma Mia!
Grant told the Daily Mail: "We were doing a scene in which Mrs Thatcher walks down a corridor with a group of ministers. Between shots, Meryl, still suited and bewigged as Mrs T, sang the Abba hits.
"It was so incongruous and hilarious and it sums up her humour and sense of mischief. It's naff to say it, but Meryl makes you feel better about yourself."
Earlier this year, it emerged that a scene from the film will include a dream sequence where Thatcher dances with husband Denis as well as Ronald Reagan.
> First Look: Meryl Streep as Margaret Thatcher