This is Franke Clarke’s second model of “The Briton” that he produced. They were manufactured between 1931 and 1939 although advertisements were still seen up to 1956. Thus production may have resumed after the end of the second world war. If not, there must have been a lot of pre-war stock still available. It’s hard to think that would be the case if they were recycling steel for the war effort. 
In all, Frank produced four different models of the Briton. Each is a typical pop-out pistol design where the barrel is pushed into the pistol to compress the mainspring and lock the piston against the trigger sear. At the breech is a threaded breech seal pin. This pin is removed so that a dart or pellet can be loaded into the breech. The pin is then reinserted which not only seals the breech but also pushes the projectile past the transfer ports at the breech end of the barrel.
There are two variants of this pistol indicated solely by the different markings. The variants are either marked “The Briton Made in England” along with a bulldog motif on the top of the pistol just ahead of the rear sight, or marked “The Briton” with the bulldog motif in the same place with “Made in England” stamped on the rectangle on the right-hand grip. There are also two variations of the bulldog image. One with a flat chin with rounded ears whereas the other has a pronounced point and pointed ears. The former being of earlier production and rarer. Both variants were only produced with a blued finish.
These pistols bear a striking resemblance to a similar pistol produced by Diana in Germany known as the Diana 2. However, the Diana pistol was manufactured from 1930 to 1938 which predates the Briton. Cosmetically, the differences between the two pistols are not only the manufacturer’s stamps and the name but more significantly the design of the grip where the Briton has ribbed grips and the Diana pistol has smooth flat plates. One other difference is that on the Briton, there is less metal rolled over the frame at the breech when compared to the Diana. 
Mechanically, most of the parts of the two pistols are interchangeable. However, the barrels and pistons vary significantly. The breech seal threads are different as are the muzzle nut threads. The piston design is significantly different where the Briton is a one-piece design and the Diana piston is constructed of two or three smaller washers sandwiched between two larger diameter washers. Both barrels are brass however, the Diana has a shoulder at the end of the muzzle thread. A washer sits between this shoulder and the end of the barrel shroud. The purpose of the washer is to protect the end of the shroud from the spring. This washer isn’t present in the Briton.
Other than the Diana, two other pistols exist that are both cosmetically and mechanically identical to the Briton except for their brand markings. These are the Milbro (ca. 1936), the Limit (ca. 1930s to 1950s) and the Garanta (ca. 1933 to 1939). 
who made the Briton?
The big question is, who made the Briton and its siblings the Milbro, Limit and the Garanta? Diana may have produced another die and manufactured the pressed steel parts for Frank Clarke. Certainly, Diana did not manufacture the barrel, piston, beech seal pins and muzzle nuts. This is something that Frank could have done in his factory easily. However, the Garanta, whilst very similar, does not have ribbed grips. Instead, the grips are similar to the Diana, but not entirely and on which the brand name of the pistol is embossed. This would have necessitated another die. Whereas the Limit is identical to the Briton other than the brand name which implies the same die could be used for both the Briton and the Limit. The Milbro also has ribbed grips but with the brand stamped into the rectangle above the ribs. This may have been stamped after the body was manufactured using the same die as used for the Briton and the Limit.
We do know that Milbro purchased airguns from Diana to distribute in Great Britain before the second world war. Perhaps Milbro requested that Diana manufacture the Diana 2 in a form that they could brand as their own. Diana may have also approached other British airgun makers and distributors to offer a similar service. However, you would expect that if Diana was making pressed steel frames for various British retailers they would have also supplied the piston and barrel assemblies.
That leads us to the possibility that a British company was sourcing the pressed steel parts from Diana, branding them for various retailers and fitting their own piston and barrel assemblies. However, this doesn’t account for the Garanta! It is possible that whoever distributed or retailed the Garanta wanted something slightly different from the other similar pistols that were available. They may well have requested Diana produce this for them. One thing is for certain, the Garanta is very rare which implies not many were made. The cost of the pressed steel parts manufactured from a unique die would have been costly. This could explain why the Garanta is so rare. Expensive parts either make expensive pistols which would have made it less competitive than the Briton and its counterparts.
It is also possible that a British company was manufacturing the pressed steel components instead of sourcing them from Diana. They may have purchased the dies from Diana under license to produce the parts themselves. It’s unlikely that they made their own dies otherwise you would expect to see other variations between the Diana made parts and British made parts. The purchase of dies from Diana wouldn’t have been cheap and whoever was producing the parts would have wanted to ensure a return on their investment. One such way to ensure they made that return would be to offer various branded versions to different retailers as appears to be the case with the Milbro and the Limit.
That still begs the question of who made the pressed steel parts. This is anyone’s guess. However, we do know that Frank Clarke produced the Britannia air pistol in ca. 1931 and the Super Briton ca. 1930 that were both of pressed steel or part pressed steel construction. No other such pistols of those exact designs have been made or retailed under another name. Thus it may infer that Frank Clarke had the means to make, or have produced for him, pressed steel parts and might be the source of all of the British made pressed steel Briton style air pistols of that period. 
One thing is for sure, most of you probably don’t care who made what. The other 0.1% will no doubt be discussing this and adding various theories until some documented evidence is eventually discovered if at all.
Until next time, happy shooting!