When Britain votes in a general election on July 4, one person will likely know the outcome before anyone else.

John Curtice, a professor of political science at the University of Strathclyde in Glasgow, will spend Election Day with his team, honing the findings of a national exit poll. At 10 p.m., before any results have been counted, he will make a big, bold prediction that will be announced on national television: the winner.

“The lovely thing about the period between 10 o’clock and 11.30 p.m. is that nobody knows!” said Professor Curtice with a grin, raising his hands into the air. “It’s that moment when we don’t really have a government.”

While he is right that no one will know the final tally until results roll in from Britain’s 650 constituencies, in the past six general elections his team’s exit poll has proved strikingly accurate, correctly predicting the largest party every time. In five of the six, the margin of error for that forecast was five parliamentary seats or fewer.

That record is part of what has made this 70-year-old professor, with his formidable intellect, unruly tufts of white hair and infectious enthusiasm, an unlikely media star. But his beloved status in Britain goes deeper. He’s frank and scrupulously nonpartisan, making him a rarity in an age of polarization — a trusted source of information across the political spectrum.