Boosey & Co.
Thanks to Nadien L in the southwest of the UK for these pictures!
This evidently is before Hawkes came on the scene. Nadien has found that this dates from between 1906 and 1911. Clarinets around that time frequently had LP stamped on them, for Low Pitch (= A=440).
The location is stamped “London, 295 Regent Street.”
I love the rollers, and Nadien says this plays very nicely.