hi..looks like a W.F. HOLDSWORTH model .. ZEPHYR ..sold one last year if i remember that seat cluster and lug pattern dates it within a few years..google it & see what comes up..good luck
So from what I can tell, the fluted seat stays appear in 1957...
...but my lugs are different, they're Nervex Pro I do believe? I haven't found a Zephyr with Nervex Pro lugs yet.
The closest frame numbers I can are a 1955 Cyclone - frame no. 18144 & a 1958 Typhoon - frame no. 25003. So my frame no. 18806 would suggest around 1956 wouldn't it?
So maybe it is a Holdsworth Zephyr, late 1956/early 1957, with the fluted seat stays but with the Nervex Pro lugs like on the cyclone (which the Zephyr took over from, right?)
Does this sound about right?
So I suppose my 18806 could well be 1957.