It took six months, thirteen days, 914 rounds of the game, and 1263 unique incorrect guesses, but finally, the remaining voice to the "Who's On Heart" competition was identified (past posts here and here). The person? Former Vice President of the United States Al Gore.
I was shocked twice this morning, the first occasion being to discover that the competition was over, and the second was learning that the last voice, the person saying "on", was Al Gore. After subsequently hearing "on" a couple more times and listening to it in context with the rest of the spoken sentence I could tell that the voice was Gore, although he was not someone I had ever considered for the voice. Kevin Taylor was the person to correctly guess Gore and he has won an impressive £60,000 with his answer.
As far as I'm concerned, I am satisfied with the competition: Tina Turner, Al Gore, and Joely Richardson are a diverse trio and I think they were a well-chosen group. Not everyone agrees, unfortunately, as I have read trolling comments in regards to Gore being one of the three (some people saying that he's not a celebrity to a few others whining about the person being an American politician rather than a British one), but most people don't seem to have a problem and are glad the competition is now over.
The three voices, both the individual words and the sentences they were used in, can be found on the Heart website: here's the link for Tina Turner, for Al Gore, and for Joely Richardson.