Peter Taylor's three part series investigates the new al-Qaeda which has emerged in the aftermath of 9/11 and the US-led invasion of Afghanistan. It examines what is known about the nature and the extent of the threat posed to the West.
You can read your comments here about the second programme in the series, the Drug Dealer, the Estate Agent and the Telephone Man, which focuses on the Madrid bombings.
The views expressed on these pages are not necessarily the views of the BBC. The e-mails published reflect the balance of opinion received.
A very interesting and informative programme, although it could do more to show the motivation of the bombers. We had to understand Nazism and Communism in order to defeat these evils, although that didn't mean we had to arrange our foreign policy so as not to offend them.
David Bannen, Oxford
Yet again another fantastic programme - each one causing more concern and enlightenment. The images shown in last night's episode lead me to believe that the UK (and European) police forces shoulg be granted further powers of stop and search. How can a human being with free thoughts and will-power lead themselves to perform ritual sacrifice? Makes you question who is the infidel.
A question that has not been answered - what are the Muslim communities doing to address the serious communication breakdowns between the 99% of peaceful Muslims and the fanatical fundamentalists? Especially following Mr al-Massari's comments in the first episode.
Andrew Moore, Leeds
I now know something about how but nothing about why.
Jack, Trowbridge, Wiltshire
What I thought tonight's programme established so well was that the Madrid bombers, rather than being the ultra-zealous Muslims one would imagine such Jihadis to be, were in fact little more than common criminals. Left unanswered, however, is quite why they espoused Islam at all?
Andrew Bradley, St Andrews, UK
Interesting programme. It showed how difficult it is to fight an ideology as opposed to an organisation. It showed that al-Qaeda as an organisation doesn't really exist. It showed comprehensively how Western foreign policy in Muslim and Third World counties has, and will continue, to generate terrorist attacks.
It was also interesting to note that Bin Laden has hit all 23 of his targets. It is a pity that the same can't be said for the West despite our best efforts. The Spanish didn't give in to terror - they just recognised that bad foreign policy was making them unnecessary targets, so they removed the bad policy.
Steve S, London
This could have been an interesting programme but it suffered from appalling production as did the first episode. The interview with General Abizaid was almost unwatchable. Did the cameraman have the DTs? To reduce such a fundamental issue to the level of a pop video is inexcusable. The current fad for "reconstructions" is banal and detracts from any interest the programme may have. They add nothing other than to pad out those parts where the programme has little, or nothing new, to add.
Chris Ban Heerden, Stourbridge, England
I found it very interesting that the Madrid bombers were planning many other attacks after the first wave, despite the Aznar government being replaced at the general election and Spain's Iraq policy doing a complete about-turn. This only goes to show that it is not even possible to give in to terrorists - Spain gave in (by changing it's Iraq policy) and yet the Madrid bombers were intending to attack again. The lesson: Iraq may have been a motivating factor, but these young men have subscribed to a wider viewpoint that is diametrically opposed to the Western way of life.
Nick, Southampton, UK
I enjoyed Taylor's jibe at the expense of Adam Curtis' tendentious Power of Nightmares, and I would be interested to know where internal BBC opinion lies on this disagreement.
Personally I think Taylor's treatment is overly dramatic but much closer to the truth - which is that the world faces a threat from pathetic but extremely dangerous Jihadis, and that we have been either asleep or pretending that it wasn't as bad as all that. Now at least we have learned the hard way that it's a real threat, while Curtis did us the disservice of telling us our fears were drummed up by governments in order to keep us pliant. Thanks a bunch, mate.
Oliver, London UK
I admit that that I had never heard of the Takfiris - Islamic extremists who "act Western" even to the extent that they involve themselves in organised crime, in the belief that this is justified in order to achieve their Islamist objectives.
This is a source of considerable concern and alarm. There are many Muslims in Europe who are, for better or worse, "Westernised". Will they now be vilified or looked on as potential Takfiris?
Ken Westmoreland, Croydon, UK
I missed The New al-Qaeda part 1 and was looking forward to being informed about this topical organisation in Part 2.
But I could only watch 10 minutes. What on earth was all that drunken camera work about? I felt ill and switched channels. Keep it simple BBC.
Adrian Furniss, Farnborough, Hants
May I congratulate Peter Taylor and all the producers involved in the three-part programme and for BBC Two for airing this brilliant piece of television. Thank you, at last, for not under-estimating the intelligence of the British viewing public. The programme has so far been extremely informative and extremely well researched. Its approach has become spectacularly relevant in light of the recent London bombings.
However I do feel that the programme contributes to the climate of fear because it seems to imply that al-Qaeda and its rogue cells are mutating without any kind of state intervention whatsoever. This imbalance needs to be addressed. Why don't you make another programme on the recent London terrorist attacks?
Ruth Jackson, London
Another important and thoughtful documentary from the BBC. However, not for the first time, the comment that "the terrorists had won" was used in relation to the Spanish general election result, directly after the Madrid bomb. Comments like this strike a very bad note.
It is at best far too simplistic. The prevalent view I have encountered in Madrid is that there had been a slow erosion of government support leading up to the election. Perhaps the election result in Spain does warrant closer inspection, but until then generalisations like this would be best avoided. It is an insult to Spanish bravery following the bombings.
Vince Smeaton, Hornchurch
Quite an interesting insight into the world of Islamic fundamentalism. The problem, though, is that it merely focuses on events alone and scratched the surface of the root causes behind them. That does not do justice by any stretch of the imagination to the issue at hand and in which context we should perceive it. We all know more or less what happened in Madrid and now London, but we understand very little about where it's coming from.
It is not rocket science; rooting out terrorism involves 2 basic steps; a) eliminating the perpetrators, and b) addressing the causes why people are lured into it (it is not fancy for people to blow themselves off on a whim). I guess the bottom line is that we are in this together so let's use our strength to fight this effectively using people of all communities and background. We may disagree at first but eventually we, not politicians, are able to solve this.
Fadel Galal, Leamington Spa-UK
I am confused as to what the BBC's agenda is in showing this programme - sensationalism or public interest? We assume that would-be bombers are au fait with all the things you show on this programme, so what is it telling us (the viewer) - to be even more vigilant, or something else?
It certainly serves to distress those who travel in London every day. My viewing of this programme was followed by Newsnight where a fundamentalist group al-Gharabba had air time on the BBC. The BBC is the only channel I watch. I applaud the quality of programming but I seem to remember in the dim and distant past the IRA were muted on television. Is it right to give these supporters of terrorists airtime or is it a matter of time?
NR , London
In my personal point of view, I am confident that the so-called Muslim extremists are not Muslims, myself being a Muslim. I think that TV programmes like this must clearly state that such so-called extremists do not represent Islam the religion or the Islamic community.
I have looked up the correct definition and "Muslim extremist" can be said about a Muslim who spends most of his time in the mosque, reading the Koran, helping and being kind to people, building and not destroying. Dear sir, I would rather they be called outlaws.
Zeyad Al-Saleh, Kuwait
Religion is the root of all evil.
Jim Long, Chippenham UK
A really enlightening series. Peter is a very brave man who deals with people in an unbiased and informative way. I can only say my heart is with all the people who have suffered. God bless.
A very inflammatory documentary and this has been released in a calculated manner to cause maximum damage to the Muslims and bolster the growing Islamophobia hysteria being whipped up by the right wing. You are alienating the vast majority of Muslims who are the pillars of British society and contribute to its well-being; Islamophobia will force these people into a corner and this, coupled with Blair's foreign policy, will only serve to make this cornered group into tigers.
Dr A R J Alvi, Coventry, UK
While this programme was a revealing insight into the workings of al-Qaeda in the lead-up to the Madrid and Casablanca bombings, I'm not convinced by Peter Taylor's assertion that there is a "new" al-Qaeda. He claimed that it was a loose movement of cells not linked to so called "masterminds". This was followed by a claim that one of the Casablanca bombers phoned Mullah Omar shortly before the attacks there, and that a meeting had been held in Istanbul to organise the attacks. Among those present at the meeting, according to Taylor, were representatives of two major figures in the al-Qaeda network, Abu Musab al Zarqawi and Osama Bin Laden. Surely this is evidence that the terror network is still run from the top, by so-called "masterminds", and has not really changed at all?
Mark Browne, Glasgow, Scotland
Casablanca, Madrid and (presumably) London bombings: relatively sophisticated organisers recruiting from disaffected Muslim youth. Politicians parrot on endlessly: "war against terrorism", "we will not give an inch" etc etc, but they miss the point. What on earth is wrong with our society that young men, invariably glowingly described by their neighbours, are prepared to blow themselves and countless others up? Should we not look at why these young men appear to be so easily recruited?
Mitch, Lytham, UK
I watched the programme with curiosity and found the complacency of the Spanish police unbelievable, as if they had searched the bombers' secret premises, the Madrid bombings could have possibly been averted.
My father was born in Iran and brought up in a strict Muslim environment. But he has stated many times there were never any teachings of jihad or holy war. Where has this come from? The older generation is confused and ashamed, I think.
I will watch next week's edition as well.
Karim Tabrizi, London, UK
Please continue to provide such thought-provoking but not deliberately inflammatory programmes - although please leave out the Mitchell brothers voice-overs for people who clearly don't talk in such a way!!
R Conchie, Oxon
It seems to have been a very naive assumption on the part of the authorities to assume that al-Qaeda would not evolve and change their methodology to suit the terrain in which they were operating just as I believe it is naive to assume that all cells are operating in the same manner. There is a weak link to every chain. I must congratulate Peter Taylor on a riveting series thus far. Looking forward to the next instalment.
Ken Buckley, Cork, Ireland
Usual dumbed-down format with totally atrocious camera-work which told us nothing at all. Not even sub-titled. It would have been better in a half-hour slot on radio. I am really disappointed in you, Peter Taylor, one whole year to compile this, and you, a serious investigative journalist (or so I thought.) What a waste.
Penelope Ross, Lyme Regis, UK
No justification is or will ever be made for acts of terrorism in Islam whether in the holy Koran or the prophet Mohammed's hadiths. Killing innocent people is condemned by Islam.
The people involved in the Madrid bombing were living lives of the rich and in luxury, some of them were clearly educated; the question we need to ask ourselves why did they do it? My answer is because the Spanish society look down on Arabs and Muslims in general, and they forgot about their pre 15th century country's heritage and link to the Muslim world.
Youssef Aldzirri, Birmingham
Why did you claim that Spain's decision to withdraw from Iraq was a victory for terrorism? In fact it was a victory for democracy in that it reflected the will of the Spanish people. It was the invasion of Iraq that was a boost to terrorism because it created the conditions for extremists to flourish.
Alan Dyer, Staines, UK
Very good programme. Why can a TV reporter work all this out and our secret service not do so? It's no good deporting them because they were born here. And anyway there are no border restrictions for people entering and exiting.
Ying-Hui The, London
Peter Taylor has a certain chutzpah in taking a pop at The Power of Nightmares. His own film doesn't have a tenth of the analytical power, original journalism or story-telling ability. It must take years of training to take such potentially fascinating material and turn it into 22 carat cliché. Three themes - awestruck interviews with various second rate cops and military apparatchiks - the tireless reiteration of the phrase "The New al-Qaeda" without any attempt to explain what, if anything, it means, plus more visual information than I need about the gloomy Mr T's physiognomy, wardrobe and gait.
Patrick Matthews, London UK
I found this programme to be informative but it didn't go into any explanation why the Madrid bombers did what they did. I think it is important to try to understand this.
Tonight's programme is a worry, not because of what it revealed about these twisted individuals, but because it showed very clearly what our intelligence communities DO NOT know.
James Franklin, Maldon. Essex