Martyn,
There used to be a once a year gathering of motorcyclists at Westminster - giving the chance for those non-motorcyclists to experience a pillion ride (i.e. those in either house, plus extras, who were PTW riders had a chance to show non-riders how 'good' motorcylcing could be).
I don't know whether these events still continue, but it might be an obvious chance to demonstrate the total difference between an M3W and a PTW?
Cheers,
