In a radical experiment which he called "building without foundations", he skipped the concrete substructure and instead built the guest wing on a pre-existing natural rock formation.
The company has said it is mainly interested in mining in areas of rock between existing flooded mine workings, but some of those flooded areas need to be pumped for safety.
"The simple fact is that the chancellor has made it clear that all existing deposits in Northern Rock are fully backed by the Bank of England and are totally secure during the current instability in the financial markets, " he said.
He and his family had already built lighthouses from Wolf Rock in Cornwall to Ceylon, and when he surveyed Fastnet, he quickly realised that the existing tower was built on the wrong part of the rock.