The Willis Faber building by Norman Foster, early 1970s won more architectural awards and fuss when built than almost any other, but I haven't heard a good word locally, nor one to add. http://www.fosterandpartners.com/projects/willis-faber-dumas-headquarters/
I don't know how many of the cosy staff interiors and roof garden are still in use, maybe there will be an open day in September