You can practice in the US with MOST UK law degrees, except the GDL I believe, they require a certain amount of time (years) to apply to sit the bar exam, and the GDL does not meet that criteria... at the very least you will have to read an LLM degree at a US university, in order to qualify.
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.