If you're into that kind of bag, Brooks and Barbour make Brompton bag$:

BAGS Brompton
https://www.barbour.com/barbour-x-brompton

just commute? only bring a cell phone, OK,

but even the O Bag, Ortlieb-Brompton is on the small side & the Straps securing the flap too short, to overstuff it and close the flap.

So I had to add a 2nd bag on the seat post, to have room for my rain gear..





....

I've seen it in the flesh, and pawed it. Believe me, it's beautiful. And around $400.

I have the O bag and added 2nd bag off the saddle for a tube and rain cape. It works out well and yes the O bag is nice. I got mine off the auction site at a small fraction for new.

Hey BadMother.

I did see one comment from you regarding modifying the Brompton block, but it sounded like a lot of work. Heck if I just have to drill some holes, that is no problem.

I tend to block out threads that aren't about Dahon Curve's or Crius'. LOL

Holy crap that is a nice brooks bag. Doesn't look water proofy enough for my city.

It is a bit more than drilling out holes, you need to carve into plastic and make sure you do not remowe more than needed (not making it too weak). I remember jur claiming it is 1/2 hour job. That is a bit optimistic, I spent some hours but it is just a matter of being patient and I`d say you need a Dreml or similar.

For us who own both bikes it is a good way to reduce the amount of bags you need.

https://www.bikeforums.net/search.php?searchid=2309995

I used a Dremel and it only took a few minutes to widen the holes enough to fit on a Dahon/Tern.

Some pics found on the Net:
Sac avant de marque Brompton sur un autre vélo pliabe (Dahon, Birdy,...) - Page 1

Thanks Winfried, that is a great thread on modifying the Brompton blocks for various bikes. Good to see a Dahon Curve as the first example.