Last night's sensational developments may have brought Britain closer to a real moment of truth about its success as a multicultural society, its tolerance of diversity and the underlying state of relations in what police like to call "the community".
For many people, obviously, the testing moment came last Thursday morning, and in the hours immediately afterwards, as Londoners of all faiths and none famously shrugged off the terrorist assault and vowed to continue their lives as normal.
From his first reaction to the bombings Prime Minister Tony Blair - like Queen Elizabeth, Metropolitan Police commissioner Sir Ian Blair and opposition leaders Michael Howard and Charles Kennedy - vowed that British values and the British way of life would endure. And, crucially, that the bombers would not succeed in dividing the peoples of Britain.
And at the conclusion of yesterday afternoon's dramatic press conference at Scotland Yard Andy Hayman, the assistant commissioner in charge of special operations, hammered home the same message.
The bombings, he declared, were the work of "extremists and criminals", on which basis "no one should attempt to smear any community."
The prime minister's all too evident anxiety - like that of President Bush in the immediate aftermath of the September 11th attacks in the United States - was to embrace the overwhelming majority of law-abiding Muslims and stress that the fundamentalists who had flown into the Twin Towers were adherents of a perversion of the true faith of Islam.
And Mr Blair was gratified on Thursday by the speed and clarity with which Muslim leaders in Britain - and leaders in local communities across the country - joined the chorus of condemnation for those responsible for the terror attacks in London.
Even as police investigated a number of racial incidents, including attacks on mosques, the relief was palpable in Whitehall throughout the weekend that the bombings had not resulted in any significant or orchestrated backlash directed at the Muslim community. However, the possibility that "home-grown" British suicide bombers carried out Thursday's attacks on the capital had already led last night to a discernible darkening of the mood in parts of Whitehall and elsewhere.
Mr Blair is expected to hold urgent talks with Muslim leaders in advance of almost inevitable calls for still clearer and more consistently articulated leadership from within the Muslim community to those who might draw inspiration from last week's bombings.
The prime minister will certainly not be "demanding" in spirit in his talks with Muslim leaders. In the Commons on Monday his approach was characterised in the declared intention to bolster their moderate leadership.
However, there will be no doubt inside 10 Downing Street that the revelations from the continuing police investigation have raised serious new questions - and seriously raised the stakes for all the people of Britain.
Mr Blair totally accepts that there is genuine revulsion among the great majority of Muslims for what has happened. But he and Mr Howard may well use Prime Minister's Questions in the House of Commons today to stress that it needs to be constantly repeated.
For both also know that tension, fear and suspicion will have dramatically increased among Britons already disposed to believe that, while the great majority of Muslims are peaceful and law-abiding, "there is a dangerous minority who feel no sense of loyalty to this country".
That finding, from a full 64 per cent surveyed for a YouGov poll at the weekend, came alongside a 70 per cent agreement that it might be necessary for the government to restrict the liberties of terrorist suspects even if there is not enough usable evidence to charge and convict them.
The Conservatives led the condemnation of the far-right British National Party yesterday for using a photograph of the bombed No 30 bus on a leaflet for tomorrow's council by-election in Barking, east London.
And a united political establishment at Westminster will be praying that police are right in suggesting that the weekend killing of a Muslim man in Nottingham was not connected to any London-bombings backlash.
The Guardian reports this morning that Kamal Raza Butt (48), from Pakistan, was visiting family and friends and was first called "Taliban" when confronted by a gang of youths when he went to buy some cigarettes.
Muslim leaders said last night that the killing would inevitably heighten anxieties in their communities, which were already high, while welcoming the fact that police have made a number of arrests.