Re: Who is John Harrison (Possible SPOILERS or Insane Babbling)
Lisbon, Portugal in DS9 was the location of a major Starfleet facility as well as part of Earth's global power grid. London is a much bigger city so perhaps major Starfleet offices and installations are there as well.
Remember what cooleddie74 says, kids:
"Don't forget to have a Patrick Swayze Christmas!"