Exiled preacher Omar Bakri Mohammad attacked the Olympic silver medallist from Bolton for wearing the Union Flag in the boxing ring.
He said Amir was 'not a good example for Muslims' and that the wearing of the Union Flag was 'a sin'.
But MPs, community groups and religious leaders have stepped in to defend him against the cleric's slur.
Conservative leader David Cameron - who described Amir as a `hero' and a `role model' when he officially opened his gym in Halliwell in January - said Khan was 'a great British citizen'.
"To call Amir Khan 'ignorant' and 'deviant' for waving the Union Jack is not just laughable, it's also deeply offensive to the thousands of Muslims who cheer Amir on in his title fights," he said.
"Amir is both a proud Muslim and a great British citizen. No one I know is more entitled to wave our flag, both because of what he does for British sport and for what he does for our society.
"As for Omar Bakri, his rant reminds us why we're so much better off without him."
Amir Khan - who is counting down to his next fight in nine days - has declined to comment, but his promoter, Frank Warren, said: "Like any decent person in this country, I am shocked and annoyed by the comments directed at Amir.
"He likes to keep his religion private and personal but I know that he is extremely proud to be British and represent his country in the boxing ring and he is equally as proud of his Pakistani heritage."
Achieved
Mr Warren said that as well as having achieved `great success' as a boxer Amir had done much for the local community.
Dr Brian Iddon, Labour MP for Bolton South East, said the exiled preacher was 'completely out of order' for his comments about the boxer.
And Salford MP Hazel Blears, who is Communities and Local Government Secretary, said: "This latest rant is beyond the pale and people of all communities will see it for what it is - hate-fuelled nonsense.
"Amir is a credit to this country and exactly the kind of role model our young people need. Like many people in this country, he is both proud to be British and proud to be a Muslim."
Khan Moghal, chief executive of the Manchester Council for Community Relations, said: "Bakri is totally wrong. He is presenting a very Medieval face of Islam that has got no relevance in the modern day.
"Amir Khan is a credit to the Muslim community and to Britain."
And Yaseer Ahmed, manager at Bolton Council of Mosques, said: "Amir Khan is entitled to wear what he wants. There's nothing wrong with expressing a British identity. The Muslim religion doesn't stop you from being British."
Amir, from Bolton, started to box competitively when he was just 11 years old.
And in 2004 he won a silver medal when he represented Britain in the Olympics.
He is an ambassador for the NSPCC and has put £700,000 into the building of a gym in Halliwell, designed to get local youngsters off the streets and interested in sport.
Last month he was named Sports Personality of the Year at the British Asian Sports Awards.
On April 5, Khan will meet Martin Kristjansen in an eliminator for the WBO lightweight title at the Bolton Arena. Tweet

Comments
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How has this become news? The views of a radical cleric who does not live in Britain. What next - "man in Russia dislikes English tea"?
What is the point of this story?
I agree! This shouldn't be a news item.
The media are part of the problem here - sensationalising these stories and further polarising opinion on the whole Islam argument.If we just ignored radicalised views such as this, they would eventually lose their affectiveness. As a civilised multicultural nation, I find that the media pandy to these stories which then provides the oxygen for the flames of distrust between Muslim and non-Muslim alike. We are not helping anybody by listening to them.
Amir Khan is a Muslim - he's also a British Citizen. If he wants to wear a Union Jack, that's his right. The cleric - we should simply ignore him. But that must start with websites like this ceasing these stories and providing a platform for those who wish to cause problems.
I find LEEP'comments contradictary and self defeating .The website exists because people are in constant need of news. If he believes that the website causes the problem then why does he contribute to it let alone use it.I suggest before you put finger to keyboard in future LOOK BEFORE YOU LEEP.
It's a fair point. People do need news - I just don't think they need to hear about what some one, who is trying to drum up further unrest, thinks about what a British sportsman chooses to wear.
And I contribute to this story because a) I'm in work and bored and b) I wish to voice an opinion.
So what's your take, selfexiled?
Leep You have made another admission of your need for sensationalism and some form of mental therapy. You say you are voicing your opinion,well I believe that is what the cleric is doing but MEN allows him to have an opinion in thier media as you have yours courtesy of their media Thats my take.
Try for a 3rd time.
The reason instances like this need to make the news is.
Religious fanatics such as this man thrive with thier radical views to promote hatred, racism, terrorism, genocide, etc, etc. Resulting in world wide terror for thousands if not millions of innocent people.
His comments regarding Khan are a springboard to the next level.
Omar Bakri is nothing more than a publicity seeking maverick. Amir Khan is a good role model for all our young people. He has done so much for community relations in our country. There is no contradiction in loving Britain and being a good Muslim, Islam teaches you to love your country. Keep up the good work Amir and good luck with your world title fight we are all with you!
There are people out there who need genuine help and support and all Omar Bakri can go on about is Amir Khan wearing the British flag.He obviously has nothing better to do with his time. I am British and Muslim and proud to be both.