The excavation took 16 months of 24-hour working to complete and required the sinking of a 65ft shaft, from where workers carved out the passageway and lined it with reinforced steel and sprayed concrete.

a claim of ownership

They planned for the worst, bringing lots of emergency supplies.

Today the ubiquitous cabin cruiser seems to many a Sunday skipper like nothing more than a watertight version of the car he left parked at the marina.