Conservative leader David Cameron has called for a ban on "preachers of hate" entering the UK.
Mr Cameron warned against visitors to the UK "sowing division"
He accused Gordon Brown of dithering over Islamist cleric Yusuf al-Qaradawi, after reports that he is to be allowed to visit London for medical treatment.
Mr Cameron called Mr al-Qaradawi - and the head of Hezbollah's TV station Ibrahim Moussawi, who recently spoke in Manchester - "dangerous and divisive".
People were in the UK "preaching hatred and sowing division", he added.
Speaking at the first meeting in London of a working group between the Conservatives and the main German centre-right party the CDU, Mr Cameron called for a complete ban on Islamist political movements Hizb-ut-Tahrir and Hezbollah.
He also said: "It's clear for reasons of our security that we must expel or refuse entry to those who preach hate, pit one faith against another and divide our society.
"So I call on the government to confirm that it will not be giving al-Qaradawi permission to enter this country and that it will not repeat the mistake of last December and make clear that Moussawi is not welcome in the UK."
Mr Cameron said the UK's national security and international credibility had been harmed by a "failed" multiculturalist policy.
He said of Mr al-Qaradawi. "He has been banned from the USA since 1999. He is opposed to secularism and believes that the penalty for homosexuality is death.
"And he has defended the use of terrorism in Israel and Iraq.
"Despite this, news reports say that it's been recommended to the government that he be given permission to enter the country.
"I've said it before and I will say it again. People like al-Qaradawi and Moussawi are dangerous and divisive and should not be allowed in this country. Full stop."