Japanese securities house Nomura already has the taste for über-security with its futuristic Jetsons-style capsule, which is the back door, but the discovery of an ancient filing system deep within the brick walls of its London headquarters in St Martin's Le-Grand has taken its policy on security to new levels.

Builders busy knocking down an internal wall at Nomura last week came across a stash of scrolls dating back to 1530 when Nomura House was part of the Mansion House estate.