I just did a bit of experimenting with stripping the paint and I'm leaving it in the sun with a healthy coating of bleach and salt on the test section while I go MOT the big stuff. Hopefully it'll do something.
update: ground off paint from top tube, treated with bleach and rubbed a load of salt in. Leaving it out overnight to grab moisture, but took pic so far...
[attachment=3]rust_day1.jpg[/attachment]
... also finished rebuilding a freebie CB ravana for partner. Just needed cheapie rear mech, new rear spindle and rear pads. Total cost of the bike: £15.50...