Murphy Tunnelling have made serious money over the years, selling virgin London clay in bulk as structural fill and capping material. The M25 took imported fill from the main interceptor sewer renewals of the mid-80s
The clay from the Jubilee Line Extension went as capping at the Greenwich site, for construction of the Dome
''the stopes soared beyond the range of our caplamps' - David Bick...... How times change .... oh, I don't know, I've still got a lamp like that.