Markeaton Interceptor (Flo Selecta), Derby

The Markeaton Interceptor, also known by urban explorers as Flo Selecta or Captain Birdseye’s Flo Selecta, is a major underground flood relief tunnel in Derby, UK. Officially named the Northern Flood Relief Culvert, it was built in 1938 following severe floods in 1931 and 1932 that inundated large parts of the city.

This stormwater culvert is designed to divert excess water from the Markeaton and Mackworth Brooks, which normally flow through the city center. When water levels rise, the system channels overflow into a 2.2 km long underground tunnel that runs east beneath Derby, eventually discharging into the River Derwent at Darley Park.

The tunnel begins near Markeaton Park, where each brook has its own inlet system with weirs to regulate flow. The two brooks merge inside the culvert in a large chamber, then pass through a long, straight tunnel with periodic vertical shafts reaching up to eight stories to the surface.

Constructed primarily of brick and concrete, the tunnel is around 4 metres high and was upgraded in 2006 to better manage increasing water demands. Despite its utilitarian purpose, the interceptor has gained attention among urban explorers, who admire its vast chambers, symmetry, and scale. The nickname "Flo Selecta" is a playful nod to its function and adds to its underground mystique. Today, the Markeaton Interceptor remains a critical part of Derby's flood defense system, protecting the city from potentially devastating high water events.