By Dominic Casciani
BBC News community affairs
This is the nightmare scenario that nobody in British society wanted to face.
The police investigation is focused on suspected suicide bombers
Anti-terrorism officers have not actually used the words in public, but the massive nationwide investigation into the London bombings is one now focused on suspected British suicide bombers who believe their faith justifies their actions.
But this is not just a nightmare in terms of the threat of violence from within, the fallout in the coming weeks and months will have the capacity to severely test - perhaps in some cases test to breaking point - the cohesion of British society.
So why does it make so much difference that the bombers are, as now suspected, British?
In the hours after the bombings, Muslim leaders in the UK, joined by other faith leaders, senior police chiefs and ministers, launched an action plan long prepared for such an attack on British soil.
That plan focuses on keeping communities together by very publicly and loudly saying all that can be said to differentiate between British Muslims and those who would seek to use a faith to justify atrocities.
WEST YORKSHIRE RAIDS
1. 0630 BST: Two houses raided in Beeston
2. Two houses raided at same time in Thornhill, Dewsbury
3. One House raided in Holbeck
4. 1320 BST: Controlled explosion in Burley
The strategy relied to some extent on the public seeing terrorism as a "foreign" threat - just as in years gone by the IRA threat could be presented as something that came from the unique, alien circumstances of Northern Ireland's sectarian society, rather than something that sprang from ordinary folk in ordinary neighbourhoods.
But the revelation that the four London suspects were British will confirm the worst fears of many Muslim leaders.
The four years since 9/11 has seen an extraordinary growth in Islamic identity in Europe. This has almost certainly benefited many communities which have, paradoxically, found a more confident voice amid the spotlight on their faith.
Many Muslim leaders point proudly at younger generations who have increasingly carved out a unique British-Muslim identity, taking the best of Islam and grafting to it many elements of European thought.
But at the same time, there has been a simmering anger which has become more and more visible in the wake of Britain's controversial anti-terrorism laws and the Iraq war.
In some cases, this is expressed through politics - such as George Galloway's sensational East End victory at the General Election on an anti-war ticket.
In other cases, it is religious with small radical groups mushrooming here or there, declaring Muslims must choose between Islam and British society.
Shahid Malik, one of Labour's Muslim MPs and probably the best placed among them by virtue of age to gauge the mood of younger generations, has said before there is a sense of double standards and injustice among some, particularly over foreign policy towards the Palestinians.
But he also says quite frankly there is a nervous reluctance among Muslim communities to admit extremism exists - much in the same way many white people cannot confront racism.
There is however plenty of evidence already of how the process of radicalisation works - the most telling from Tel Aviv in April 2003.
It was then that two British young men, Asif Hanif and Omar Sharif, carried out a Hamas-organised suicide bombing, killing three.
The pair met at university and, it is thought, got involved in radical Islamist student politics where the perennial issue is the perceived injustice of Israel's conflict with the Palestinians, and the West's alleged hypocrisy. These groups can be catalysts in alienation, presenting Western culture as immoral and incompatible with a literal reading of holy texts.
Suitably inspired, they headed for Syria where, officially continuing their studies, they joined Hamas and made the leap from talk to fatal action.
In many respects, their profiles fit that of the 9/11 hijackers: these were young, educated men with good prospects.
In their minds, the decision to bomb was philosophically rational, based on an analysis of how they believed Muslims are treated - and the responses open to them.
Backlash fears grow
So what happens now? If the apparent British suicide bombers are of similar stock - young British-born men who are not driven by desperation, then British society's ability to deal with this may be severely tested.
This is what Muslim leaders fear most.
Firstly they fear there will be a severe backlash against ordinary folk going about their business (women in Hejab headscarves are commonly targeted in hate attacks).
Suicide bombers: British men Omar Sharif and Asif Hanif
But just as importantly, they fear that reaction may, in turn, create deeper divisions in society - and create more opportunities for those seeking to radicalise the young.
Anxiety levels are up across the country and if this turns to anger then it could have an immensely destabilising effect.
Take the 2001 Bradford riots, for example, which had everything to do with a corked bottle of pent-up anger that exploded on the streets.
Crucially, the clashes themselves are popularly thought to have been triggered by white racists deliberately provoking young Muslim men to fight back. And when they did, the situation quickly got out of control.
Returning to present events, if Muslim communities are destabilised by the London bombings, the implications for British society could be far greater than a hot summer night's riot.