They were originally made at the end of World War II, for issue to demobilised servicemen. They're made from old Spitfires, literally. At the end of the war there was a great shortage of all materials, except for military scrap. Aircraft in particular were an easy source of metal, as their aluminium could be recycled with relatively little effort, compared to steel. This is just one of the reasons why Land Rovers were built of aluminium, rather than steel sheet.
These were quite possibly made by Dowty in Cheltenham, or a similar maker. At the end of the war, they found themselves with an empty order book, but lots of experience in light alloy construction.
They're made of thin aluminium sheet, with the ends riveted. Originally painted green, with a couple of green stripes around the middle, I recreated these stripes with the polishing.
Polishing was easy, although the usual tedious task. I used an angle grinder with a paint stripping wheel to strip the paint, then a drill with a nylon abrasive bristle flap wheel to polish it. Afterwards a coat of wax.
Next job is a pair of ex-mil map cases. These are much harder, as they're far better painted. Two coats, with a chromate-looking undercoat, so it's tenacious stuff and the dust is a bit nasty too.