Was this a 'through' the bridge or low flying across the bridge,as i do not recall any 'media' reports for the time,nor does it seem to feature in Biggin Hill folklore.
The pilot's name was Chris Francis and his passenger was Ashley Wilkin (from the same year at school), from whom I heard the story. I know it was June/July 1970 as that's when we did our A-Levels and left school. The aircraft was (I think) from the Surrey and Kent Flying Club.
Afer emigrating to Australia to join their Army (don't ask why!), Chris returned to the UK in about 1975/6. I saw details of the prosecution in a flying magazine in 1976/7 which corroborated the story that I had been told, that it was
under Tower Bridge. I recall that the heading was "The CAA always gets its man!" or something very similar; he was fined a lot.