The folding process begins with lifting the bike by the saddle, and energically swinging the freely- pivoting rear triangle under the frame (or "top tube") in a single movement. This is also Brompton's parking position. A special spring- loaded chain retainer on the drivetrain side keeps the chain in tension at all times, thus preventing it slipping from the chain wheel or the sprocket.
    In this half- folded state, the Brompton may be gripped with one hand by the rim/tyre under the top tube, lifted up and "hanged down" by the saddle from one's shoulder when carrying it upstairs, into the shops (all of the bike is then in front of one, nothing sticks out behind, where it could crash into people or objects), or anywhere else, where full folding down is not needed.

    Total time thus far:  2 seconds.