A 14-year-old boy from Lancashire who voted in the general election said he did it because he "wanted to make a difference".
Alfie McKenzie, from Poulton-le-Fylde, voted for the Liberal Democrats in the Wyre and Preston North constituency, after being sent a polling card.
He was only caught when he confided in a teacher at school. His head teacher called the local council and police.
Ben Wallace won the seat for the Conservatives with a 15,844 majority.
Wyre Borough Council and Lancashire police have both said they are investigating.
Alfie went to his local polling station before school on Thursday, wearing a trench coat, glasses, jeans and smart shoes so officials would "think I was a Tory".
"I knew they wouldn't suspect an under-18 for voting Tory," he said.
Alfie said he was "very serious" about politics and socialism, but decided to vote Liberal Democrat as a tactical option.
He said: "There's not a socialist candidate in our area and unfortunately even if there was it would be a wasted vote. I've looked into it and the best option for a socialist is the Liberal Democrats.
"I did want to make a difference - unfortunately I didn't."
Alfie's mum, Nadine Wiseman, said she had asked him not to vote, after he received the polling card, but she "wasn't surprised" when he did.