The Big Brother race row shows an "ugly underbelly in society only too ready to point the finger at the foreigner", the Archbishop of York has said.
Dr Sentamu turned down the chance to appear on Celebrity Big Brother
Dr John Sentamu said it was everyone's duty to tackle racism from "whatever quarter it rears its vicious head".
The archbishop, who turned down an invitation to appear on Celebrity Big Brother, compared racism with the hospital superbug MRSA.
He said it was "the worst enemy because it attacks directly community organs".
His comments came as he gave the 20th Martin Luther King Memorial Lecture in London, with a call for the country to overcome and cast out "the four modern demons of our time" - idolatry, materialism, militarism, and racism.
"The events of the past week on our television screens have reminded us only too well of Dr King's famous dictum that 'ignorance is the root of all prejudice'," Dr Sentamu said.
"Sadly ignorance is not in short supply. Racism is real.
"As the week's events on reality television demonstrate, there is an ugly underbelly in society only too ready to point the finger at the foreigner, or those who might not fit in.
"But much more worrying than the soap opera silliness of Big Brother were the comments of the judge this week who, rather than chiding a defendant for racially abusive comments towards a police doctor, advised the defendant on how to insult Asian people in such a way that he didn't end up in court.
"The eradication of racism is a serious task for all of us. It isn't some optional liberal gesture towards minorities."
Iraq war 'folly'
The archbishop also disputed calls from Trevor Phillips, head of the Commission for Racial Equality, that members of the BNP should be refused communion in Church.
"Of course the BNP is wrong in its message of ethnic superiority and hatred towards all Muslims, Jews and the rest of us whom it would deport given the first opportunity, but Jesus Christ died for them as well.
"The communion table must always be open to those who are unworthy of it, and I count myself most unworthy of all to approach the altar of God."
In a wide-ranging speech, Dr Sentamu also criticised the British and US governments for adopting "militarism" as the basis for international relations.
He said the war in Iraq "demonstrates the folly of thinking that we can bomb our way out of trouble".