excavation could have the world 's first natural underfloor heating system sourced from spring water in roman drains .
the idea has been in the pipeline for years , but now excavation work has begun to determine whether it 's possible to connect a modern heating system with an ancient hot spring .
engineers plan to excavate ancient crypts below the church to tap into a roman drain where 850,000 litres of natural spring water empties every day into the ground .