A model range that was produced by Curzon over an extended period between the war years. The earliest date-able example (2nd from top in the picture below) is from 1924, according to the box it arrived in. Also from the late 1920's is the top pen, a Mottled 'red ripple' flat-top, that was fitted with a warranted 14ct gold nib.
3rd from top is a later flat-top leverfill that is almost certainly not the Mottled HR it is intended to resemble.
4th looks to be a very early example, noting the Pat Applied For and the "sun" logo on the clip.
5th A later Button Filler, which I think was also the basis for some of the Lang produced Regent and own brand models (such as Rufford). See below for another pen of similar style:
The Levers on the pens in the top picture are of interest. The black pen carries the "shamrock logo" which is also seen on many of the Rosemary Pens sold by British Carbon Papers. This might suggest that Lang were the manufacturers of these small and highly collectible pens.
The Tan coloured mottled pen has a lever that carries a sun logo. There are many no-name / own brand pens out on ebay that are wrongly attributed to De La Rue. This may suggest that Lang were the manufactures of many of those pens.
The early packaging was pretty functional:
There is nothing to confirm that the box below was original to the pen
But then the matching pencil was also unbranded