Humphrys could have been 'clearer' over AV says BBC
The BBC has said Today presenter John Humphrys could have been "clearer" about how the alternative vote works during an interview with David Cameron.
Mr Humphrys told Mr Cameron it was incorrect to argue that some people's votes could be counted more often than others under the system.
In response, the prime minister said the presenter was "completely wrong" and should go "back to school".
A BBC spokesman said the disagreement was part of a "lively" exchange.
The argument came less than 48 hours before voters decide whether to change the way MPs are elected.
Voters will be asked whether to stick with the current first-past-the-post system, in which voters select one candidate and the individual with the most votes wins, or switch to the alternative vote, in which voters can list candidates in order of preference if they choose.
Under the AV system, if one candidate gets more than half the votes, they are elected straight away.
If not, the candidate with the fewest votes drops out and their second preferences are handed out to remaining candidates.
This process continues until someone gets over half the votes, or no more votes can be distributed.
The dispute during Tuesday's interview came after Mr Cameron said the current system was "simple, fair and decisive" and under AV "you start counting some people's votes more than once".
Mr Humphrys said this was "simply not true".
Mr Cameron replied: "Yes you do. You count all the votes and then you start eliminating candidates and then you count people's preferences."
The BBC presenter continued: "And I have a second preference as well as you or anybody else and you count them again as well, so you don't count some people's votes more than others."
The prime minister said this was not the way the "complicated" system worked and that the interviewer was "completely wrong" but Mr Humphrys suggested the process was, in fact, "terribly simple".
Pressed again, Mr Cameron replied: "If you vote for a Labour candidate and I vote for a Monster Raving Loony candidate and the Monster Raving Loony comes last, my second preference is then counted again."
When Mr Humphrys replied "so is mine", the prime minister said he "didn't understand the system" he was explaining.
"It is quite worrying if actually the lead broadcaster on the BBC does not understand the system," he added. "I do think that is worrying. Back to school."
The two men clashed again minutes later when Mr Humphrys suggested first-past-the-post was used by "no other major democracy". Mr Cameron said he was "absolutely staggered" by this and insisted that the system was used "by half the voters in the world" including in the US.
The official "No" campaign in the referendum have claimed AV would undermine the principle of "one person, one vote" that it says has underpinned British democracy. It also argues that only three countries around the world use AV.
The "Yes" campaign have said AV would more clearly reflects the range of voters' views, is used to elect Labour and Tory leaders and that first-past-the-past has been not been used by any devolved UK legislature set up since 1997.
In a statement, the BBC said Today and other programmes had "spelled out in great detail how AV would work" if introduced.
"During a lively Today interview, David Cameron and John Humphrys disagreed over a technicality when the AV referendum was discussed," a spokesman for the corporation added.
"John Humphrys was trying to reflect the point of contention between the campaigns over whether some people, in effect, have more than one vote under AV.
"In hindsight, he could have made this clearer".