David Cameron has blamed getting his favourite football team wrong on "brain fade".
The Prime Minister said he supported West Ham United during a speech in south London when he is in fact an Aston Villa fan.
Outlining his 2020 vision for black and ethnic minority communities, he told supporters: "This a country where people of all faiths, all colours, creeds and backgrounds can live together in one place.
"We are 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."
Asked to clarify his loyalties after his speech, which he read from an autocue, Cameron replied: "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."
The two football teams play in the same colours but that is where the similarities end.
The Conservative Party confirmed the football reference was not included in the Prime Minister's prepared speech but was an off the cuff remark.
Cameron's blunder was omitted from the official transcript of his speech issued by the Conservative Party.
But it was swiftly seized upon by his political rivals, as the hashtag #villagate began trending on Twitter.
Labour's former communications chief Alastair Campbell - whose own team Burnley also play in claret and blue - said the mistake "says a lot about his character which impacts upon policy. Out of touch. Phoney. Believes nothing."
Campbell said every sports fan would have their "stomach churning" to hear the PM apparently forget the name of the team he supported, adding: "I am sorry but this alone means Cameron has to go. Total million percent phoney, as (Villa manager) Tim Sherwood might say."
Shadow chancellor Ed Balls, a fervent 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, a fellow Villa supporter, said he believed the mistake was down to an error in Cameron's speech.
"PM is a passionate Villa fan. Takes son to matches ... Suspect speechwriter error," said Collett.
Soon after the prime minister's gaffe Comedian Matt Lucas took to Twitter, creating an amusing new team name.
He posted: "David Cameron just remembered his favourite football team is Weston Villham."
While former England footballer Gary Lineker posted a video of the "brain fade" and wrote: "David Cameron has forgotten which Football Club he supports. Aston Villa last week, West Ham this. Burnely next?".
When he was first elected to Parliament in 2001, Cameron said he did not follow football, telling the House of Commons in a debate on hooliganism that year: "Many of those who have spoken in the debate or have written about the subject are either lawyers or football fans, but I have to confess that I am neither."
The first mentions in the national press of Cameron's liking for the club came after he was elected Tory leader in 2005. He was reported in 2006 to have written on his blog that he "half-heartedly" supported Villa and could name only three of their players. His uncle Sir William Dugdale, who died last year, was the club's chairman from 1975 to 1982.