Could this maker's mark possibly be "G.C.P. Co" rather than "G.D.P. Co"?
 
If so, then it seems probable that it's from the Clyde Pottery company,
Greenock (pronounced 'gre-nuk'), near Glasgow, Scotland.
Note that Glasgow is also the most likely candidate for the partially illegible
third line.  According to Godden, marked pieces from the Clyde pottery
"probably date from c.1850-1903".  Godden also cites J. Arnold Fleming's
_Scottish Pottery_ as a source for further information.
 
 
On Mon, 28 Sep 1998 16:55:25 -0400 James G. Gibb wrote:
 
> A local amateur archaeologist asked me about a piece of late 19th/early
> 20th-century white earthenware bearing the mark below. I am unfamiliar
> with ceramics of this period. I would appreciate hearing from anyone who
> might be able to identify the maker's mark.
 
> G.D.P. Co.
> Porcelain
> [?]LASGLO[?]
> [three wing-dings]
> Warranted
> M [encircled)
> CHINA
>