The UK's atheist biologist Richard Dawkins has defended the right of Republican presidential front-runner Donald Trump to say that Muslims should be banned from entering the US.

"Horrible though his views are, free speech is more important," Dawkins said on Twitter.

Dawkins is himself outspoken on Twitter about Islam and the left's response.

More than 500,000 people have signed a petition on the UK Government website to ban Donald Trump from the UK, five times the number needed for it to be debated. This is a record for the government's petition website. Parliament considers all petitions that get more than 100,000 signatures. Home Secretary Theresa May has declined to say whether she will ban Trump from entering Britain. 

The petition says: "The UK has banned entry to many individuals for hate speech. The same principles should apply to everyone who wishes to enter the UK.

"If the United Kingdom is to continue applying the 'unacceptable behaviour' criteria to those who wish to enter its borders, it must be fairly applied to the rich as well as poor, and the weak as well as powerful."

Trump's campaign has been widely condemned for calling for a "total and complete shutdown of Muslims entering the United States until our country's representatives can figure out what is going on."

Republican Jeb Bush claimed Trump is "unhinged." The White House said he should be disqualified from running for president. 

Earlier this year, Dawkins and HBO host Bill Maher said it was "ridiculous" that some make Muslims out to be a "protected species."

Dawkins said: "So they think that if you criticise Islam you're being racist and you're absolutely right that the regressive give a free pass to Islam. They're kind of right about everything else, I mean, they're right about misogyny and all of the other good things. But in the case of Islam, it just gets a free pass and I think it is because of the terror of being thought racist."