Thanks, Alan. The Siddeley Special was a model made between about 1934 and 1938. I think they were supposed to show off the companies advanced engineering, or On the car there's no mention of Armstrong, all the badges being Siddeley Special, or S6, so maybe it was because JD Siddeley was retiring, he would have been about 65 when the model launched. Most of the bodywork is aluminium as is the engine block, head and con rods. It's got hydraulic valves, which I think was quite advanced for the time. It was basically the biggest, most expensive model in the line-up at the time costing about as much as a 4 bed house in London. The other models were all known by their RAC HP rating, eg 12HP, 14HP, 16HP and 17HP. The Siddeley Special 5.0 litre engine, was RAC rated at 30HP, which is roughly 110BHP.
About 253 were made but being made of aluminium, quite a few got donated and scrapped for the war effort. Worldwide there's about 22 extant about half of those are roadworthy.
My dad bought this one in 1997 and although he didn't make much progress with it before he died in 2015, he was always dreaming of the day he could drive it. I promised him I'd get it back on the road and have spent the last four years restoring it. At about 1:43 in this video you can see what it looked like six months into the restoration. Maurice Smith, RIP, helped with panel beating the wings and it's been a feature of the club's stand at Stoneleigh and NEC restoration shows for the last few years.