Buying US stocks In my Barclays stocks and shares isa?

Hello, I have some money in my Barclays isa and want to invest in US stocks. Most probably the s&p500 but also thinking of putting the bulk into google. My question is do I then pay US tax even though it’s through my uk stocks and shares isa. What’s the best way to get the decent returns of the US stock market being a uk citizen. Barclays do an adventurous fund but it’s not as good as the S&P, would any one consider Barclays adventurous fund? Thanks for the help