Jules Verne’s classic novel Journey to the Centre of the Earth might need updating now that Swedish solar lighting firm Parans has developed 100m long cables that technically allow full spectrum sunlight to be transmitted 30 floors down into the ground. Verne had an eye for the future, but even he couldn’t have predicted London property values being such that the well-to-do might prefer to luxuriate in a jacuzzi deep underground rather than floating in a hot air balloon high above it.