I may have misinterpreted but are you looking to chuck the Tesco CC miles into your UK account and then transfer the miles to your USA account ?

I'd have thought that having multiple accounts dilutes your mileage worth as it takes longer for each account to gain enough miles to be worthwhile. And the risk of BA finding out and closing all your accounts and you losing all your miles would probably put me off.

I think the suggestion of moving the HA to the UK is probably the best one.