Slow Horses season 4 on Apple TV+ has viewers wondering if Slough House is a real MI5 branch. The British spy thriller is based on the bestselling Slough House series of novels by Mick Herron. Like the source material, the series centers on Slough House — the istrative purgatory for MI5 agents who've made career-ending missteps. Although these "slow horses" are relegated to drudgery, they get involved in high-profile cases, thanks in large part to the rude-yet-incisive veteran MI5 agent Jackson Lamb (Gary Oldman), who leads Slough House's team of well-meaning misfits.

Although the ensemble is led by Lamb, Slow Horses' other key characters include River Cartwright (Jack Lowden), an MI5 agent who lands in Slough House during season 1 after making a very public mistake, and Diana Taverner (Kristin Scott Thomas), the Deputy Director General of MI5 and head of operations who's been gunning for MI5's designated "First Desk" since the show's start. With its often-bumbling band of agents, the Emmy-nominated series is a refreshing twist on the spy genre. However, that doesn't necessarily mean Slow Horses is an accurate depiction of MI5, its processes, or its operatives.

Slough House Is Not A Real MI5 Building

Herron's MI5 Purgatory Is A Fun Invention For Slow Horses

Contrary to popular belief, Slough House is not actually a real MI5 building — nor does any branch resembling Slough House exist. While the TV series has adapted Herron's novels pretty faithfully, making a few Slow Horses is not accurate to MI5, which, given the "slow horses" constant blunders, might be for the best. Being relegated to office work might be a real thing, but there isn't an entire department at MI5 dedicated to paper-pushing operatives who've bungled prior cases.

If the offices on Aldersgate Street in London actually existed in the real-world MI5 organization, it would say a lot about the agency...

There's no denying that the antics of Slough House make for great television, but, in real life, a counter-intelligence and national security agency probably wouldn't want to put the nation's fate in the hands of people who could cost civilians (and fellow agents) their lives. A misstep might get an MI5 agent pulled from the field, but a grave blunder would likely see them losing their position altogether. If the offices on Aldersgate Street in London actually existed in the real-world MI5 organization, it would say a lot about the agency — and not in a good way.

Slow Horses Does Mention Real Aspects Of MI5

The Unconventional Spy Thriller Isn't A James Bond Movie

Even if the non-existent Slough House means Slow Horses episodes still have the show's MI5 agents involved in much more high-stakes field work than the average operative. At the same time, the series does a better job than most espionage thrillers — perhaps because of its Slough House premise — of showing the dull side of the job, with agents pushing through istrative work and IT issues.

Slow Horses Uses (Some) True Story Inspiration

The "Tiger Team" From Season 3 Is Based On Fact

Regardless of how well it depicts MI5, Slow Horses does base some of its plot points on true stories. In season 3, MI5 higher-ups order a "tiger team" to abduct a member of Slough House to stress test MI5 and uncover any weaknesses. In government and military agencies, tiger teams serve as a form of quality control and allow agencies to solve ongoing issues. The Slow Horses season 4 will continue that trend.

New episodes of Apple TV+'s Slow Horses season 4 air on Wednesdays through October 9, 2024.