From those numbers it looks to be 1918. I don't have a lot of W&P bikes on my list from 1918, but a lot from 1919 onwards.
If anyone has any W&P engine, frame and registration numbers then please send them to me. I have been compiling a list of data since I bought my 1913 TT model and have 69 W&P bikes from 1910 to 1925 at the moment (plus a much shorter V-twn list).
Swindon Branch Secretary
Ariels - 1913 TT Model, 20 Roadster, 28 Model D, 30 Model B, 38 VH, 52 VH
The Offroad Fleet - Bultaco Pursang, Beta Rev 3