Where should I study Law? Watch
You would have to check with Harvard if they mind you studying Law in the UK first. Though really, what's the point if you don't intend to practice in the UK? You'd have to relearn everything in the US. Plus you wouldn't even be qualified to practice in the UK because you'd still have to take your LPC/BPTC and your training contract.
If they say they don't mind you studying Law in the UK first, then do that, because you'll need a backup if you don't get into Harvard, or if you change your mind.
Does it have to be Harvard or nothing? Would you still prefer to study in the US if you couldn't go to Harvard?
You would finish with an LLB and JD allowing you take prepare for the bar exam of whichever state you fancy.
Hope this helps !
That is hurdle number one... additionally you can only take the bar exam in two states, NY State and California. Most other states require a law degree from a US institution. Both of these states have reciprocal agreements with most if not all other states, for admittance to practice law once you have passed their exam, but be aware, NY State and California are the hardest bar exams to pass.
Before you embark on such an endeavour, it would be wise to research attrition rates and actual passing rates.