From the sound of it, you really want to use this trip to boost your existing BA account, but if you have any reason next year to be in the USA, you might consider joining AAdvantage.

Check out the American Forum and do a search for "Platinum Challenge". Or find FewMile's "unofficial AAdvantage website". Register for the Challenge and once you hit 16K, you are oneworld Sapphire/AA Platinum (next to top tier) but also you get 100% mileage bonus on all further miles for the year. This means the additional 24K you accumulate on this trip will actually clock in at 48K. Since you don't fly USA domestics, the upgrades will be of little use, but I have heard that non-US residents can have these changed to international upgrades using an appropriate equivilency. You are likely to build up enough miles on this trip to qualify for a J-class UK-USA ticket on AA or BA, particularly if you register for some route bonuses that are sure to exist if AA is one of your carriers along the way.

You will likely also accumulate enough miles (50K) early enough in 2001 to requalify for this status through February 2002, i.e. two years.

And of course, as a Sapphire, you have access to BA and all the other oneworld lounges (except ironically, AA's NAmerican ones), if you don't already have that benefit as BA Silver.

Just a thought, but obviously your other travel plans for 2001 should determine which program you want to maximize you benefits and/or mileage with.