Speaking at the BAFTA Awards - where she received a Fellowship - Mirren said: "The National Youth Theatre at this moment in time is incredibly important because the way my business is going, it's the prerogative only of kids who have got money."
An NYT graduate herself, Mirren said the organisation "was my way in because we [my family] didn't have money to send me to drama school."
In response, the NYT's artistic director Paul Roseby told WhatsOnStage: "Dame Helen Mirren is absolutely right that free alternative routes into the industry are more vital than ever before and she is a shining example of the benefits we reap when we invest in the best of young British talent."
Last year Roseby launched the NYT rep company, a free eight-month "talent development initiative" culminating in a three-month West End run.
"All of last year's company signed with agents," Roseby added, "and around half have already worked professionally since they finished in December - proving that there are legitimate affordable routes into the industry.
"However we echo Dame Helen's call for more support so that these kind of free opportunities can be extended to many more young people, especially outside of London."
Mirren is the latest in a line of actors and industry figures to caution about acting becoming an elitist profession. Speaking in 2012, Julie Walters warned that "the way things are now, there aren't going to be any working class actors".
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