No not Ariel and the engine dusn't look like J.A.P. ider.
I would say a Swis engine so maybe an 500cc "Alp" motorcycle 1905? made in Alperton- Londen.
It looks like a 28 inch rearwheel and 26 front, a home made handlebar and footboards, a Triumph frontforks.
The rear tirevalve has an angle so he will have a flat tire within 10 miles.