I'm American. My grandfather (on my father's side) was born in Yorkshire, England around 1902 (my father really doesn't know when he was born and we don't have a birth/death/marriage certificate). My grandfather moved to Canada at around 15 years old and later joined the Canadian army to fight in the last days of WWI. He then emigrated to the United States and became a naturalized citizen. I called the British consulate and they said that I could not become a British citizen. Could he have renounced his British citizenship when he became an American? Why did the British consulate say I could not become a British citizen?