Tinie Tempah follows two homeowners who are digging down on their quest to unearth extra space. In Hertfordshire, one couple plan to double the footprint of their Grade II listed gate lodge to the size of three double decker buses with an enormous subterranean extension. The second one - an £11million basement in the heart of Knightsbridge - was home to ballerina Margot Fonteyn and the former Panamanian Embassy.