It looks like its going to be a postwar James ML model, a 125cc. ?
http://cybermotorcycle.com/gallery/james/images/James_1947_ML_125cc_in_The_Motor_Cycle.jpgNot very much of it there or useable really, is there !
For something that was an economy lightweight model, with very limited road riding ability these days, you sure you want to continue with this - they are not very expensive to find complete and running.
And the one you have there looks to have other problems - the frame downtube (under the seat) looks to be gone, completely !!, and someone has added those two plain steel straps to replace it. So its missing the rear engine mounting.
You will have a lot of work finding all the missing bits, and be quite expensive to do this way. And, sorry to suggest this, but it would make good spares for someone looking for forks, or wheels.
HopethisHelps.
P.S. There were also quite a lot of these made in wartime. e.g.
http://miliblog.co.uk/wp-content/gallery/british-ww2-preserved-motorcycles/james-ml-military-lightweight-125cc-1943re-9889.jpgIts possible yours has been civilianised - although shows no sign of this (for whats left, anyway).