Hi Mr Nick -- I had exactly the same thing when coming back through France last year. I had liberally sprayed gold-colored chain wax the day before so thought the loverly sparkly effect on my swing arm was that... until closer inspection showed it to be metal filings from the hub!!!
Had to get towed to a local Ducati dealer in Reims, who despite neither of us speaking each others language, got the hub assembly ordered in and fixed it up in a couple of days. (I wasnt that dissappointed as Reims is a loverly place to to spend a couple of sunny days relaxing!!)
Worked out OK actually, as the AA covered all the labour costs, so I had only to pay for the parts... couple of hundred quid I think.