This sort of thing is why I always run a GPS track when I fly anywhere. The track is kept for some months in the Garmin 496, till the next flight (say a week later) if I am running Memory Map (UK VFR flights), and indefinitely if I am running Oziexplorer (all foreign flights).
If one was picked up for a falsely alleged bust, the only data
they will have is a radar track, which could be out a fair bit, or intermittent, and you will need your super accurate GPS track log to get yourself off the hook.
However my guess is that the CAA does not follow up marginal busts - they are not stupid and they know that the pilot probably has a GPS track which in a marginal case any half good lawyer will be able to show is far more accurate than radar. The lists of CAA prosecutions (on their website) make it obvious that most busts are not followed up. Just as well - I did a little one last year myself (phoned up and apologised)
