For others' benefit: On a 2021 Brompton, the Litepro B-series clamp didn't work with a "9 Speed Front Derailleur Folding Bike Double Gear" LitePro derailleur, because on a double crankset, the fork sat too far outward and wouldn't reach the inner chainring. It might be because I turned a triple into a 46/30T double with the outer ring removed.

I had better luck with the NC-100/Meijun/Mi.Xim clamp, but still had to install the derailleur a bit astray for the fork to reach the inner ring.

So, it's really a combination of a crankset, a clamp, and a derailleur. YMMV.