Hi johanna My father was resident in England since the age of three (1914) and he and his brothers were all called up into the Royal Dutch Army in England from the time that the Netherlands were invaded in WW2. One of them was killed in Europe rather later. I don't know what the official designation may have been, but there was certainly an active quasi Dutch War Office in London. Whatever my papa was doing, it did not, I think hugely involve Americans. He had big issues, not often expressed, about how desperately stupidly Dutch Resistance personnel in Occupied Europe were treated by officials in the UK.
He certainly spent a bit of time square bashing in Conway and, apparently, eating boiled sausages, but I have no idea about the brigade or regiment. Given that he had a congenital deformity to his hip – over a year in traction at the age of eight, doing his lessons on his back – that was never resolved, I doubt if he was the Dutch equivalent of the SAS or Navy Seals.
The hallmarks are hard to see – one on the lid and one on the base – but I think the assay office is London, which would make sense.