In 2017, when Brompton had the bottom bracket recall*, I replaced my stock bottom bracket with a UN55. The SKU was 4524667778790, and it's listed as part number BBUN55B18. I've been riding it with this bottom bracket for the past 6 years with no issues.

This is a 68 x 118 British thread square taper. I don't recall having to do anything special, such as add a spacer, to make it work.

*I bought it from Clever Cycles in Portland, but live 150 miles from there. I wasn't about to drive it to Portland to have a free replacement installed.