 Britain's greenest city has launched a hunt for virtually free hot water more than a mile below its central streets. Drilling has started in Newcastle Upon Tyne on a borehole which hopes to tap inexhaustible supplies of groundwater naturally kept at 80C (176F) by geothermal heat.  The project, based at the former home of the city's most famous previous liquid - the old Scottish and Newcastle brewery - expects to tap the water and start pumping in early June. By then, the drill operated by scientists and engineers from Newcastle and Durham universities will have reached 2,000m (6,500ft).  The ?900,000 project is confident of pumping out enough steady supplies to heat the 24-acre Science Centre, which has replaced the brewery, and large parts of the city centre. Newcastle's main shopping mall, Eldon Square, is expected to be an early customer, using the recirculated water to heat 140 shops.  The Newcastle project is part of a programme which earned the city top place in the Forum for the Future's 2009 and 2010 sustainability tables. The borehole, funded by the local Newcastle Science City partnership and the Department of Energy and Climate Change, follows a successful trial of geothermally heated water in Upper Weardale, County Durham.