Reporting back:
joftek, thanks for going to the trouble of posting your route. We set off with the idea of using it. I printed out the cue sheet, but as the printer is somewhat borked, couldn't print off the accompanying map. And I failed to study thje map in detail before we left.
Oops.
So we got to Borrodaile Road and decided it ended in a dead end, so spun round and eventually found ourselves on Garrat Lane. Couldn't see signs for Girdwood Road ( the next on the list), tried asking my phone the way, but couldn't hear it over the traffic, so ended up in Wandsworth on the A3. Ho hum.
Bike route toaster seems to miss cues when it goes off road, so no pointers for heading into parks or going on contra flow cycle lanes. No matter. I should have prepared better. And it was a grand day out.