Kevin McCloud marks the 100th episode with one of the programme's most ambitious projects to date. Leigh Osborne and Graham Voce want to convert and extend a landmark 150-year-old water tower in central London into a luxury home. Grade II listed, derelict and with 6ft-thick walls, it's a huge challenge for the pair, who also plan to build two structures at the base - a lift shaft connected by a series of glass tunnels, and a modern living space. The result will be a four-bedroom property over nine floors, complete with a room at the top offering spectacular 360 degree views across the capital. The tower, which is located directly above London Underground's Northern line, was originally built for Lambeth Workhouse in 1877 and became a Grade II listed building in 2008.