Lots of great ideas - thanks all!

Re: adding to the start rather than the end of the route - I'll look into giving it some sort of weighting towards the last point added.
A turn sheet is something I've wondered about adding to the end of the PDF. There's a slight technical complication (I won't bore you with the details) but it shouldn't be impossible. Will take a look.
@andrew_s: thanks for spotting - looks like Flot (the charting library) needs extra support for IE8. Shouldn't be hard to fix.
@Ben: definitely not ORS - I don't think ORS is fast enough to do draggable routes. I'm running a heavily customised instance of
OSRM with cycle routes, elevation, surfaces and a bunch of other stuff added on.
Out of interest, what's the NCN/A-road location in question? I can at least check that the route is marked as mud in the OpenStreetMap source data, though it may not change anything.
@Wunja: one day! But it's UK-only for now, I'm afraid - not least because some of the data (the OS OpenData) is UK-specific.