To anyone who had a problem with the odometer in their 307 reading more miles than actually travelled, Peugeot now have a fix.
I was phoned up last week and asked to bring my car in for "a download from the internet". It appears to have fixed the over-clocking, but the number of miles displayed hasn't been reduced. I estimate that the odometer is displaying over 1000m more than I've done in the last
6 months.