Could MI5 have stopped the London bombings?

Tomorrow sees the publication of two major official inquiries into the 7 July suicide bombing attacks in London in which 52 people were killed, along with four terrorists. One, by the Commons Intelligence and Security Committee, will examine whether there was a failure of intelligence, while a "narrative" by a senior civil servant instructed by the Home Office will give a "factual breakdown" of the events leading up to the attacks.

Both reports will be stripped of material deemed to be operationally sensitive or likely to compromise security. Other material will be excluded for legal reasons. The net result is an incomplete account that will do little to stifle calls for a full public inquiry. Among the key issues are:

Should the intelligence agencies and police have known about the plot?

MI5 argue that while it was disappointing that they did not prevent the 7 July attacks, they could not have done any more to prevent them. The agency insists that when they came across two of the bombers, Mohammad Sidique Khan and Shahzad Tanweer, they were peripheral to the case of a separate bomb plot. MI5 says it had limited resources and had to prioritise its targeted suspects.

While both official reports are expected to say that the intelligence and security services were not to blame for failing to prevent the bombings, they remain vulnerable to criticism.

The fact that MI5 and the police had prior knowledge of two of the four bombers was only disclosed in December by The Independent. It later emerged that Khan, the ringleader of the bombers, came under surveillance on a number of occasions and visited a training camp in Pakistan. Both men were thought to be involved in low-level crime to raise funds for fighting abroad.

Can lack of resources be blamed?

The reports are expected to say that MI5 only had the capability to investigate a small number of terror suspects. Westminster sources have suggested privately that there were only a few dozen MI5 officers trying to deal with hundreds of Islamist suspects. This is denied by the security service.

MI5, MI6, and the Met's anti-terrorist branch are all undergoing expansions. MI5 has seen its workforce grow by about 500 to 2,500 since 11 September 2001, and this is due to rise to 3,500 by 2008. Of last year's intake, 14 per cent were from a black or Asian background.

Is there an al-Qa'ida "Mr Big" involved?

No evidence has been found to support the idea that the suicide bombers were directly influenced or directed by an al-Qa'ida commander, and the reports are due to back this assessment.

Like most of the terrorist cells uncovered in the UK, they were a self-contained team.

Embarrassingly for Tony Blair, the reports, especially the one by the Home Office, are expected to say that Britain's foreign policy in the Middle East, including the Iraq war, was largely responsible for motivating the bombers. Khan and his fellow bombers, Tanweer, Hasib Hussain, and Germaine Lindsay were inspired by trips to Pakistan.

A videotape of Khan released after the attacks featured footage of Osama bin Laden's deputy, Ayman al-Zawahiri. Experts believe the tape was edited in an attempt by al-Qa'ida to claim credit for the attack.

Where did the terrorists get their bombs from?

Khan, a primary school teaching assistant, used the internet to find how to make a peroxide-based explosive. The bombs were made at a house in Leeds. The ingredients and equipment to make five 10lb bombs were inexpensive and only cost a few hundred pounds.

What is Pakistan's role?

Khan and Tanweer visited Pakistan and are believed to have been in contact with Muslim extremist groups in the country. This was unknown to both MI5 and MI6.

The ISC report is expected to say that the Pakistani authorities did not pass on information about Khan and Tanweer until after the bombing. MI5 say that thousands of Pakistanis living in Britain, and Britons of Pakistani descent, go to the country every year, and it is impossible track them all.