I should have said that I have tried the insert. I found I could never get it quite right, either 5mm too high or 5mm too low. I still have both said inserts so maybe I need to give them another go, but I was wondering if there were other solutions. Is there a Brompton seat post that has markings?
If you find it a few mm out, you could always raise the saddle holder-jobby (pentaclip?) as there's easily 5mm of adjustable height on the top of the seatpost
I should have said that I have tried the insert. I found I could never get it quite right, either 5mm too high or 5mm too low. I still have both said inserts so maybe I need to give them another go, but I was wondering if there were other solutions. Is there a Brompton seat post that has markings?