The fold on the Hummingbird is woeful, though.
YMMV. I like it. It's somewhat narrower when folded than the Brompton, which makes it easier to carry by your side. It also means it slots into the gap between train seats, which the Brompton doesn't.
Looking at the released details for the Brompton, it's pretty much a direct competitor for the Hummingbird, so if the fold is a clincher for you, then obviously the Brompton wins. And of course the Brompton has the name and reputation that the Hummingbird doesn't have.
If I were shopping for a folder with £4k to spend, I would find it hard to choose. I'm unlikely to be facing that choice any time soon though.