You might assume that a founder in his eighties – with decades of success, an Oscar, a BAFTA and a long-standing team behind him – might have his feet up by now. But arriving at Cosprop on London’s Holloway Road, John Bright warns me that he’ll have to leave at three for a fitting with actor and long-time client Francesca Annis.

Bright remains involved in the costume house he founded in 1965, which has worked on a huge number of productions across stage and screen, including Downton Abbey, Emma and Game of Thrones in recent years. While he’s working in a lesser capacity ahead of retirement, he’s still the only one who knows where everything is in the warehouse, says company manager Chris Garlick, and the top-floor office is still busy, its antique table teeming with buttons and trims, books and notes. An intercom frequently announces delivery drivers arriving for pickups; “I’m sorry, I don’t know how to turn that off,” Bright says.

As Cosprop celebrates 60 years via the exhibition Costume Couture: Sixty years of Cosprop at London’s Fashion and Textile Museum, the legacy it sits on is a collection of over 300,000 costume pieces, estimates Garlick. Behind its three-storey, 19th-century building is a larger warehouse, where rows and rows of clothing span floor to ceiling and wall to wall, sorted by gender, period, season, material and colour. There are walls of boxes containing hats, shoes and lace trims, and a sparkling room of costume jewelery (“when I do tours for students I always switch the lights off,” Garlick adds).

All of which “is really the result of 60 years of making costumes. Virtually everything we’ve either made, or are originals, or pieces come to us one way or another via donations,” he says.