Robin, 
 
I imagine others will catch this also, but there is a serious mistake  
here.  Bagehot published his famous _Lombard Street_ in 1873  
and was the editor of The Economist for an extended period of time  
in the 1800s.  Quite sure he was not writing anything in or before  
1776. I don't know the earliest usage, but I know that the term  
"economist" or "oekonomist" or "economiste" was in use without  
the "political" in front in both Germany and France well before it  
was in Britain.  I would bet France was probably the first place it  
was used by itself.  BTW, I think it was in France that the term   
"economie politique," or its equivalent in whatever language was  
also first used.   
 
Barkley Rosser 
James Madison University