Three days ago Mechta posted a link to the forum where originally the photograph was posted. On that forum there are two close-ups, apparently taken from the photograph when it had been removed from under glass.The first shows the forward fuselage. The other shows the engine. On that forum there has been some debate about the letters that appear to be on the fuselage, just aft of the firewall. Some have suggested that these are part of a registration mark. I've not seen any British aircraft that carries its registration mark in that position. Some have suggested that the letters are 'NATT'. Having looked carefully at the letters, using a magnifying glass, I think that they are more likely to be 'GNAT'.
Putting aside Folland's jet, the only other British aeroplane that I associate with 'GNAT' was F.G.Miles first, abortive attempt at aircraft construction, which was built in his father's laundry in Portslade, Sussex, in 1925/26. Evidently the aeroplane in the photograph isn't that Gnat - it was a biplane - but the thought crosses my mind (and I appreciate that this is a very long shot) that possibly the aeroplane in the photograph might have been constructed from the components of Miles' Gnat after construction of that had been abandoned.
As far as I'm aware, very little is known and has been written about Miles' Gnat. The main source of which I know is Don Brown's 'Miles Aircraft since 1925' (Putnam). In that he says:
'With the help of a friend, F.Wallis, he [Miles] evolved the 'design' of a small biplane known as the Gnat. Having completed the few drawings they thought necessary, they started construction, using as longerons the ash chassis of a small sports car which Miles had been building.'
'At length, the airframe of the Gnat was practically complete except for covering with fabric. A small two cylinder engine of 698cc was bought, complete with a 4 ft diameter airscrew, still in the author's possession, which had been used in one of the aeroplanes built for the Lympne competitions of 1923.'
Broadly the same information is related by Arthur Ord-Hume in 'British Light Aeroplanes - their Evolution, Development and Perfection 1920 - 1940' (GMS). However he says that the engine was to have been a 698cc Blackburne (which strongly suggests that it was a V twin Tomtit). I've looked carefully, again using a magnifying glass, at the close-up, taken from the original photograph, of the engine of the aeroplane in the photograph. Allowing for the low resolution and concomitant lack of clarity, whilst one might argue that it has features which suggest that it isn't a Tomtit it would be a brave man who, based on that evidence, would assert that it definitely is not a Tomtit! Thus that possibility must remain.
Unfortunately I don't have Peter Amos' three volume history of Miles Aircraft and so I don't know if that contains any more information about the Gnat (if anyone reading this has that, it may be worth checking it). The intimation of Don Brown is that, with the subsequent involvement of Cecil Pashley and the acquisition of an Avro 504K, Miles' Gnat was side-lined and eventually abandoned incomplete. So could it be that the engine and propeller destined for Miles' Gnat found their way into the hands of the grandfather of the original poster on the other forum, to be used on the aeroplane depicted in the photograph, and that the propeller, at least, ultimately passed to his grandson ? If so it is difficult to reconcile the grandson's statement, that he has the propeller from the aircraft shown in his photograph, with Don Brown's assertion that he was in possession of the propeller destined for Miles' Gnat (presumably c. 1970, when his book was published). Despite this it would be most interesting to know the dimensions of the grandson's propeller (in the context of Don Brown's statement that the Gnat was to have had a four foot propeller) and how and when it came into his possession (Don Brown died in the early 1980s - what became of his propeller, subsequent to that, I don't know).