Gordon Brown has been caught describing a voter, 65-year-old Gillian Duffy, as a "bigoted woman". Here are some of the key reactions.
He's an educated person, why has he come out with words like that?
I am mortified by what has happened. I have given her my sincere apologies. I misunderstood what she said. She has accepted that there was a misunderstanding and she has accepted my apology. If you like, I am a penitent sinner.
PRIME MINISTER'S SPOKESMAN
He was letting off steam in the car after a difficult conversation. But this is exactly the sort of conversation that is important in an election campaign and which he will continue to have with voters.
GEORGE OSBORNE, SHADOW CHANCELLOR
We have found out the prime minister's internal thoughts... and I think they speak for themselves and the prime minister has got a lot of explaining to do. What people will see is the contrast between what he was saying publicly and what he was saying privately.
NICK CLEGG, LIB DEMS LEADER
Just because someone disagrees with you, it doesn't mean you should insult them... whatever people say, you should try and treat them with the respect they deserve.
LORD MANDELSON, BUSINESS SECRETARY
What will upset Gordon is the hurt caused to her. It's not in his nature to want to hurt people like that.
NICK ROBINSON, BBC POLITICAL EDITOR
It highlights a huge gap between the prime minister's public and his private demeanours
the leader of the Labour Party has insulted one of the very type of voter it's so vital for his party to hang on to - older, white and traditional Labour.
LANCE PRICE, FORMER DOWNING STREET SPIN DOCTOR
It will be endlessly talked about. It will be described as a gaffe and it was a gaffe.
PETER KELLNER, POLLING ORGANISATION YOUGOV
Those people who are fans of Gordon Brown will sympathise with him, those who don't like him will consider it a very bad thing. The question is the reaction of those in the middle... It may be that people will be absolutely appalled... But it may be that a lot of people will say he is a human, there is a lot of stress, isn't he allowed to say one thing to her in person, and then another in private?
IVOR GABER, POLITICAL ANALYST, CITY UNIVERSITY, LONDON
People know that Brown is no angel, and though this won't do him any good, it's not certain how his will play out.
GILLIAN DUFFY'S NIECE
It's disgraceful. He's just shown his true colours. He's always trying to pretend to be so nice and in touch with the people but he's obviously not. I can see it anyway. I don't like the man, to be honest.