AndrewC, I am in the process of transferring from the UK to the US program. When you submit your request to BA, they send you one sheeters on both the US and the UK programs. You can then compare how mileage/points are accumulated and can be used on each.

For what it's worth, I looked at this four years ago and did not make the move. At that point, the US program offered almost only transatlantic flights. I use my BA points predominantly for flights within Europe. The programs have now been brought into much closer alignment, and I am making the transfer.

Hopefully, someone else can answer as to whether you can use points to upgrade flights if you chose the US based program.