The Apple TV+ hit series "Slow Horses," inspired by Mick Herron’s bestselling novels and adapted for television by Will Smith, is set to debut its seventh season next year. Costume designer Guy Speranza, who oversaw the wardrobes for all six seasons, recently concluded his work with the finale of Season 6. Speranza discussed his meticulous approach in creating iconic looks for the show's main characters, including Jackson Lamb, played by Sir Gary Oldman, and Diana Taverner, portrayed by Kristin Scott Thomas. His efforts involved bespoke tailoring, sourcing, and complex fabric treatments to bring authenticity and personality to each character’s costume.

Central to Lamb's distinct presence was an extensive wardrobe of tailor-made suits and shirts, deliberately aged and distressed to reflect his disheveled, unkempt appearance despite wearing traditional spy attire. Speranza detailed the process of creating multiple copies of each costume, using methods like burning, dyeing, and washing to simulate wear, making Lamb’s look a central visual storytelling device. This deliberate “broken down” style helped portray Lamb as a revolting yet complex figure, reinforcing the "dragged through a charity shop" description from the books and contributing to the character’s memorable on-screen identity.

In contrast, Diana Taverner’s wardrobe emphasized elegance and power through sharply tailored dresses and mid-length skirts, avoiding trousers to highlight her femininity and presence in a male-dominated environment. Although the show’s original scripts described her wearing trouser suits, Speranza, with input from Will Smith, chose skirts as a deliberate statement on power and femininity. The costumes were sometimes bespoke, sometimes a curated mix, designed to maintain consistency through fast-paced shooting schedules and extensive location changes.

Other characters also benefited from Speranza’s thoughtful costume design, such as Christopher Chung’s Roddy Ho, whose eccentric outfits balanced detachment from reality without descending into caricature. Jack Lowden’s River Cartwright wore a funeral suit throughout Season 6, with the costume gradually deteriorating to mirror his character’s chaotic journey. Across all characters, the costumes evolved season by season, with Speranza carefully integrating character traits and story arcs into the clothing, making the costumes crucial to the immersive experience and success of "Slow Horses."