A petition posted on the prime minister's Web site, www.number-10.gov.uk, calling for the mosque's construction to be blocked, attracted more than 275,000 signatures before the window to sign up closed late on Wednesday.
While the number of signatories suggests strong opposition, the petition has drawn accusations of racism and Islamophobia from civil liberties groups and Muslim Web sites. The mosque's backers also point out the petition exaggerates the facts.
At a time of heightened tension after a series of Islamist attacks, the debate risks inciting deeper social unrest in Britain, which has a 1.7 million-strong Muslim community.
The online petition has turned the proposal to build a site of religious worship on empty land into an issue drawing in the prime minister's office, the mayor of London and the 2012 Olympics.
Responding to the furore, the government said it did not endorse the language used in the petition.
The petition was started by Jill Barham, a campaigner linked in the media to a far-right blog called English Rose. Attempts to reach Barham for comment were not successful.
In the petition, Barham states: "We the Christian population of this great country England would like the proposed plan to build a Mega Mosque in East London scrapped."
But even before that signature was found, the petition had drawn sharp criticism.
One criticism was that it played up facts, calling the mosque a "mega" structure that would cost 100 million pounds ($200 mln).
Those behind the mosque, a Muslim group called Tablighi Jamaat, which has 75 million members and calls itself a missionary movement, say it will cost 50-75 million pounds.
They also dismiss suggestions it will house 40,000 people, saying it is set to hold 12,000 -- which would still make it the largest site of worship for any religion in the United Kingdom.
"Neither the source of funding, nor the size of the proposed mosque has been reported accurately," said a spokesman for Tablighi Jamaat. "The group is saddened that so many people have been influenced by false information."
London's mayor, Ken Livingstone, issued a statement this week denouncing the false reports, including one saying he would fund the mosque. He said they could damage community relations.
"The particularly vicious nature of the campaign against a possible Muslim place of worship in east London should be condemned by all of those who support...freedom of religion," he said.
A statement on the prime minister's Web site said the government believed discussion of such controversial issues should take place "in a manner that respects the views of all."
While Tablighi Jamaat is largely maintaining a low profile, the debate shows scarce sign of going away.
One line of attack from opponents is that the mosque is tied to the London 2012 Olympics. In fact Tablighi Jamaat bought the land for the mosque in 1996, long before the games were awarded. But if permission to build is granted, it would open in 2012.