By Dominic Casciani
BBC News community affairs
A Muslim surgeon at one of London's top hospitals involved in the post-attack emergency operations summed up the situation.
United: Faiths came together in East End
As a man who has spent years serving Londoners, he suddenly feared the city's residents would turn their eyes on their Muslim neighbours - even though they were just as innocent as everybody else.
"Our worst nightmare has come true," he told the BBC. "I truly hope nobody has the gall to say that this was done in the name of Islam."
As thousands of Muslims throughout the capital go to Friday prayers, that fear will be shared by many of them.
One Muslim group has already called on women not to go out, predicting those who wear the headscarf could become targets for hate attacks.
Most Muslim leaders suggest this may be a little too cautious - arguing that the community needs to be seen at the heart of society.
But fears of a backlash are rife, not least because in the wake of 9/11 many Muslim communities say they have experienced hateful attacks, be they vandalism of mosques, verbal abuse in the street or worse.
The newly-knighted Sir Iqbal Sacranie, head of the Muslim Council of Britain, has met Home Secretary Charles Clarke, and community leaders are to gather on Friday evening at one of the country's largest mosques to discuss next steps.
Advice being put out includes a mixture of the cautious - choose seats on buses where you can't be trapped by a potential assailant - to the more optimistic - walk with confidence to make an attacker think twice.
The East London Mosque, just 200 yards from where the Aldgate bomb detonated in the Underground, holds thousands of worshippers every Friday and is the public face of the East End's predominantly Bangladeshi Muslim community.
Its chairman Dr Muhammad Abdul Bari said: "I have seen the resilience in this community, I know them well.
Muhammad Abdul Bari: "Community resilience"
"I believe that whatever happens we can cope with it because we have prepared to withstand such situations."
Ever since 9/11, and particularly since the Madrid train bombings of 2004, there have been behind-the-scenes plans between Muslim and Christian leaders about how to react if and when terrorism came to London.
That plan swung into action with the first statement from Muslim leaders - a joint statement with Churches Together, an inter-faith organisation.
Following Friday prayers at East London Mosque, a host of East End faith leaders gathered again for a silent vigil yards from the Aldgate attack to unite their communities and stand determined against terror. Monsignor John Armitage of the Catholic Church in east London said that he personally felt a strong bond with Muslims because of the way his own faith had been linked to terrorism.
"For many years, the IRA had a campaign of bombing, and when they bombed Birmingham I was a student in the city. Let me tell you that anybody with the briefest understanding of religion should understand that religion has nothing to do with terrorism.
"When people talked of the IRA being Catholic terrorists, they were no such thing. This is why I stand today in solidarity with people of faith, and people of no faith here in the East End."
Some extremist organisations have already started publishing material on websites blaming Muslims, or at the very least their faith, for the London attacks.
It is this expected development that will now concern Muslim leaders trying their best to ensure their community are not blamed.
Prayers across the land: Worshippers in Leicester
Many leaders fear they will face a more difficult job in protecting people if rumour and speculation about who was behind the attack makes it into the media.
But Inayat Bunglawala of the Muslim Council of Britain says it would be absolutely the wrong thing to do for people to run scared and hide away.
"It would send all the wrong signals," he said. "By all means exercise caution but people should be doing what they would normally do. To stay at home would be the wrong thing to do."
Braced for an attack
Dr Bari said the East London mosque has already received hate emails but he had also been heartened by seeing supportive correspondence.
It was this support that the mosque's Imam Sheikh Abdul Qayum emphasised during his sermon.
Tohel Miah: Fears being singled out
Addressing thousands, he said the only way to defeat terror was for communities to stand together and Muslims should feel confident in their identity.
"No religion can accept what these criminals have done," he said.
Similar messages were being delivered in mosques throughout the UK - but the news on the streets was mixed.
Many Muslims have been quietly bracing themselves for such a terrorist act and bracing themselves for the scrutiny that would come in its wake.
In the East End two young British-born Muslim women said they were resigned to suffering fallout.
"I'm just not bothered any more," said one.
"Whenever something like this happens, I know we're going to get targeted.
Last time [Madrid train bombings] I got pointed at in the street."
Her friend added: "I think the mosque leaders are right to speak out as publicly as they can and defend our rights because otherwise the terrorists will win."
Tohel Miah, 28, was among those willing to give his name, even though he was apprehensive.
"I've got a beard, and if you think about it, someone could assume I'm an Arab terrorist," he said.
"But I believe everyone in Britain will stand by us, I just hope the media do their job and don't inflame the situation."
But older members of the community clearly felt more fear.
Two middle-aged women in full veils said they would go to the mosque to say special prayers for the dead, the injured, and all the families involved.
"If there was ever a day to pray to God, then that day has come," said one.