Jeremy Corbyn's material for Prime Minister's Questions is being leaked to the Conservatives by his own staff, the Labour leader's senior aide has claimed.
In a fly-on-the-wall documentary, Mr Corbyn also accused the BBC of being "obsessed with trying to damage the leadership" of the party.
Mr Corbyn's chief spokesman, Seumas Milne, said the internal leaks took place following weekly preparatory meetings for PMQs.
Speaking after one of the weekly parliamentary encounters between Mr Corbyn and David Cameron, he said: "This time they did (know the questions) because it leaked. It leaked from that meeting.
"It's very annoying because it only happens about a third of the time, but it obviously gives them a little bit of extra time.
"Whenever there is a leak it gives them that advantage - it gives them the advantage on TV as well."
The online documentary by Vice News followed Mr Corbyn for a number of weeks as he attempted to steer the party through an anti-Semitism crisis and local elections night.
Labour lost 18 seats in the May elections, but the leader claimed the result proved the BBC had been overestimating how badly the party would perform.
He said: "The whole narrative, all day and all last night and all for the past month has been 'Corbyn's going to lose', 'Labour's going to fail', 'Labour's going to lose', 'Labour's going to fail'.
"There is not one story on any election anywhere in the UK that the BBC will not spin into a problem for me.
"It is obsessive beyond belief, that they are obsessed with trying to damage the leadership of the Labour Party and unfortunately there are people in the Labour Party who play into that."
He also expressed wider distrust in the media, blasting an unnamed group of political commentators for being "shallow, facile and ill-informed".
The behind-the-scenes look at the veteran left-winger also showed him campaigning, posing for a host of selfies and the efforts of his team to ensure he dresses smartly.