Nice find! There were dozens, perhaps hundreds of small frame building shops in England from the early 1900's on up till the 60's. The cut on the lugs looks unusual to me (though I am far from an expert) and should help with identity.

Getting a few quality photos of the frames component parts as well as the mechanical parts (hubs, cranks etc.) and posting them to this thread may provide folks with enough information to work with.

If it "as found" it is earlier than mid-50's and the headclip style stem was gone before WW2 as I understand. The serial number will only help once the builder has been found.

My suggestion is to leave the original finish in tact. The original paint is much of the value of this machine to collectors.