David Cameron has been feeling the wrath of Twitter after saying in a speech that he supported West Ham when he is an Aston Villa fan.
Shadow chancellor Ed Balls was among political rivals to seize on the slip-up, as the hashtag "villagate" started trending on Twitter.
The PM blamed "brain fade", adding "these things sometimes happen when you are on the stump".
The Conservatives said the reference was not in the PM's prepared speech.
Mr Cameron's apparently off-the-cuff remark came during a speech about his plan to increase opportunities for ethnic minority Britons - in which he said Britain was "a shining example of a country where multiple identities work".
"Where you can be Welsh and Hindu and British, Northern Irish and Jewish and British, where you can wear a kilt and a turban, where you can wear a hijab covered in poppies.
"Where you can support Man Utd, the Windies and Team GB all at the same time. Of course, I'd rather you supported West Ham."
Questioned about the slip-up by the BBC's Jonny Dymond after the speech, Mr Cameron referred to Green Party leader Natalie Bennett's explanation for her own slip-up when trying to explain her party's policies in a radio interview.
"I had what Natalie Bennett described as a brain fade. I'm a Villa fan... I must have been overcome by something... this morning. But there we are, these things sometimes happen when you are on the stump."
Labour's former communications chief Alastair Campbell was unforgiving on Twitter, writing that the mistake "says a lot about his character which impacts upon policy. Out of touch. Phoney. Believes nothing."
Shadow chancellor Ed Balls, a Norwich City fan, tweeted: "Hey David Cameron... I'm off to see that football team I support this afternoon. Name escapes me... they play in yellow... Watford?"
But former Conservative press officer Jonathan Collett rushed to defend Mr Cameron, adding: "PM is a passionate Villa fan. Takes son to matches ... Suspect speechwriter error."
Quizzed further about his football allegiances, in an interview with Sky News' Murnaghan to be broadcast on Sunday, Mr Cameron said: "I've been an Aston Villa fan all my life, I literally opened my mouth and I was going off-piste about the fact that in Britain you can be a supporter of the West Indies, a supporter of Manchester United, and a supporter of Team GB.
"I was then busking about other things you can support and was... I don't know what happened to me, it was just one of those things."
He said he had gone "off script" with the remark adding: "By the time you have made as many speeches as I have on this campaign all sorts of funny things start popping out of your mouth."
Mr Cameron said he became a Villa fan after watching the team beat Bayern Munich in the European Cup final as a child.
"But I don't go very often, in fact I haven't been for years and years, but I try and keep up, and I'm hoping we are going to escape the relegation zone, which we're out of now, and obviously the FA Cup final is very exciting."
Reminded of his comment in 2001 in the House of Commons that he wasn't actually a football fan, Mr Cameron said: "I mean, I'm not a regular attender, I used to play football as a kid, my son plays football, and I try and sort of keep up with what's happening in the Premier League and see how Villa are doing.
"But when they get snug in the middle of the table I tend to sort of, I tend to back off a bit. When we get close to the bottom I get nervous, but I don't know what happened this morning."
Mr Cameron's late uncle Sir William Dugdale was Aston Villa's chairman from 1975 to 1982.