For Flame, they should be able to use an EDL in the CMX 3600 format. Just export that from your timeline. Get in touch with the post house in London though, and email them a test EDL from your system to make sure.
Not sure about Avid, although the post house can certainly help you with that too.
Just curious, if they're shooting P2 on the HVX200, why not just FEDEX copies of the original P2 folders on external USB drives instead of dealing with the OffLine/OnLine workflow? I've been doing that fairly regularly between Munich and Vienna, and it works just fine. The cost of the drives (about $75 each for 120GB) is far less than the cost of reconforming on Flame or Avid, and eliminates a lot of potential errors. You could then send London the final project media, an FCP Project File and an EDL all in one shot (keeping backups of course as you go). For me, it's worked out a lot cheaper, better, safer that way.
hth,
Clay