Just ran a quick comparison of some programs here and it looks like the US Airways cost is only 60K points in Y versus the 70K from bmi. They often have deals where buying the points is pretty cheap, though that's still probably about $600-700 in costs, plus the need to find award space. I'd probably go for 80K on US and get biz seats if you can; a much better value. Being in the UK means you won't be able to get the US credit card and such for bonus miles and the buy miles bonus right now is only for CC holders so not as great a deal, but still cheaper than buying the BD points. And the taxes/fees redeeming from US are much lower than redeeming from BD.

Only valid on the SFO-HND route operated by JAL and only for travel through the end of February.