It's 50 years since Vice President Richard Nixon and Senator John F Kennedy made history with the first ever presidential TV debate. The idea was quickly adopted around the world. But how much do voters really learn from these encounters, and do they ever make the difference between winning ald losing? The BBC's political correspondent Reeta Chakrabarti unearths some memorable moments from the archives and talks to politicians, television producers, academics and journalists about the heated negotiations, meticulous preparation and sometimes painful gaffes which have had millions glued to their sets at election time. She also asks what Britain's party leaders can learn, as they prepare to face each other on TV for the first time.