As far as I know you can apply for them online, or arrange them through the british embassy. To be honest the only time it's come up for me is when we were travelling and a friend had the bag with their passport stolen. It does seem to be a valid route for expats to do a single visit too.

If you were visiting in 6 weeks, that would probably qualify you for an emergency passport since it ticks the "can't get your UK passport renewed in time" box. Have to agree that overall they've just made this more confusing though.