No, that’s not how international roaming works. You will dial UK numbers in their national/local format and for international calls you will replace 011 with 00.
I will explain why: when you travel to another country with International roaming activated your cell phone will get its signal from wireless networks in the country you’ll be in, therefore you will have to use the rules of this country to dial out.
On the other hand, when receiving calls people must use the whole international dialing sequence to reach you from any country except the country where the cell phone is registered. In other words, people from the UK will dial 00 1 ??? ??? ???? to reach you, while to call you from the US one will use the same dialing pattern used when you are in the US.