Gave it a good washing with Nooj's
Shiny Bike Sauce (very effective and highly recommended), then tried to get on with cleaning off the rust on the rear footpeg hangers and and repainting them.
Unfortunately the first thing I found was that the allen bolts which hold the Givi racks to the underseat pipes are pretty much solidly rusted in place, despite using Plusgas on them several times over the past few days, so on one the inner hex has rounded off and the other broke the tip off a ball-end allen key
(I'm probably going to have to either drill them out or cut a slot in them and see if I can get them out with a flat-head or maybe impact driver.
I took the rear wheel off to give good access, but then one of the bots on the hugger snapped whilst trying to unscrew it. Fortunately the rest came out ok, so I'll be able to secure it back in place.
I then found that the drill-type wire brushes were too big to get into all the nooks and crannies, so ended up using a Dremel instead which was a bit of a faff, but did the job to clean the rust off.
After some masking tape and using a cardboard sheet to screen the bike from over-spray, I put a couple of coats of etch primer on the hangers which already look better, now I just need leave that until tomorrow and then repaint them.