The name G Tester, Clapham (in Surrey) appears on the perch pole of this well made banjo.  Nothing else is known of this maker/retailer/owner, however it has all the hallmarks of a Richard Spencer made banjo dating from around 1910-15.

Bertolle sold the "B&T" model which was almost certainly made by the same maker.  Note the bracket nuts inside the pot of this instrument which are identical to both the B&T and the CE "Imperial" model of the same period .. and they both have the "Spencer" style laminated neck.