A famous place of
rendezvous for London. When a
government minister Jeffery Archer sent people here to
pay off his
prostitutes, and
MI6 sent an agent here to pick up a briefcase once "accidently" left behind by a
Soviet Diplomat.
Platform 3 is more generally used nowadays by people to meet various strangers they want to meet for whatever reason. This is why it has taken off in some internet circles as a totemic rendezvous point.
In my experience meeting anyone at Platform 3 has always resulted in a very bad set of experiences following. So I would suggest avoiding that tradition, and meet at Platform 4 at Victoria Station, or Platform 3 at Paddington Station.