Has a dolls head gearbox and fork return damper springs and later type frame, so its 1936 to 1938 style, essentially the same in those years. Looks like a 350cc ?, iron top end.
The muffler is "Brooklands Can" style, added to what looks like a long straight-through pipe (slightly unusual setup), so a bit of Brooklands runnings seems to be suggested (those 'mufflers' were required there to quieten things down for the nearby residents)
That large tank is quite special. Long distance race ?
Does anyone have any thoughts on the double floatchambers visible, now that is really unusual... ??
P.S. Great pics, thanks for posting.