The demolition of the huge, neo-classical Euston Arch in the 1960s to make way for the new railway terminus in north London, is still ruefully cited as a prime example of architectural vandalism. In the first series, Dan Cruickshank tracked down some of the masonry to a garden in Kent. Now, as the programme returns for a second season, divers are delving into east London's River Lea, hoping to raise the rest of the Arch.