Someone was asking on the procedures on removing the Brompton seatpost bung (Pre-2018 version) earlier in the day. Its really a 3 simple steps procedure. Unscrew, pop and release!
The following explains:
Better known as the titanium guy at Bike48/Brompton slimming center. Always trying to tell people titanium is 41% lighter than steel. Proactively modding up his Brompton with the leftover parts!