Jeremy Corbyn is correct in saying that there is a strong connection between the terrorist threat in Britain and the wars Britain has fought abroad, notably in Iraq and Libya. The fact that these wars motivate and strengthen terrorist organisations like al-Qaeda and Isis has long been obvious to British intelligence officers, though strenuously denied by governments.

The real views of British intelligence agencies on the likely impact of Britain taking part in wars in the Middle East are revealed in a Joint Intelligence Committee (JIC) assessment dated 10 February 2003, just before the start of the invasion of Iraq led by American and British forces. It is marked “top secret”, but was declassified for use by the Chilcot Inquiry and, though it was referred to by several publications, attracted little attention at the time.

It says, “the threat from al-Qaeda will increase at the onset of any military action against Iraq. They will target Coalition forces and other Western interests ina the Middle East. Attacks against Western interests elsewhere are also likely, especially in the US and UK, for maximum impact. The worldwide threat from other Islamist groups and individuals will increase significantly.”

An earlier JIC assessment dated 10 October 2002, also declassified by Chilcot, says: “Al-Qaeda and associated groups will continue to represent by far the greatest terrorist threat to Western interests and that threat will be heightened by military action against Iraq.”

Corbyn is saying almost exactly the same today as the JIC predicted in 2003. He cites with approval experts pointing to “the connections between wars our government has supported or fought in other countries and terrorism here at home". He adds that their assessment in no way reduces the guilt of those who attack our children, but that an informed understanding is essential in order to fight rather than fuel terrorism.

The JIC conviction about the benefits to al-Qaeda of the Iraq war was swiftly borne out after the invasion as it expanded from being a small group of militants, perhaps less than a 1,000-strong based mainly in the mountains of southern Afghanistan and north-west Pakistan, into a global movement. Al-Qaeda in Iraq, taking advantage of the destruction of the Iraqi state, developed into one of the most powerful and influential terrorist movements in history, and later transmuted in Iraq and Syria into Isis.

Corbyn says that “we must be brave enough to admit ‘the war on terror’ is simply not working”, adding that “we need a smarter way to reduce the threat from countries that nurture terrorists and generate terrorism.” Again, this is demonstrably true as vast resources have been poured into waging the ‘war on terror’ since 9/11, but Isis, al-Qaeda and similar Salafi jihadi movements are far stronger now than they were then. They have powerful military forces fighting in at least seven wars – Afghanistan, Iraq, Syria, Yemen, Libya, Somalia, North East Nigeria – as well as in insurgencies, large and small, such as in Sinai and north-west Pakistan. Individuals and cells carry out terrorist attacks everywhere from Orlando to Baghdad and Berlin to Mogadishu.

Seldom has a war been so comprehensively and visibly lost as ‘the war on terror’ and it is doing a favour to Isis and al-Qaeda not to recognise this and try for something better. Yet critics of Corbyn have unconsciously been doing just such a favour to al-Qaeda by demanding he stay silent. In a crass but unintentionally revealing interview, the Conservative Security Minister Ben Wallace claimed that Corbyn’s timing was “appalling”. He said that “we have to be unequivocal, that no amount of excuses, no amount of twisted reasoning about a foreign policy here, a foreign policy there, can be an excuse. The reality is, these people hate our values.”

Of course, this is the old political gambit, often deployed by politicians and journalists, of deliberately mistaking explanation for justification. More significantly, Wallace repeats the mantra usually expressed after terrorist attacks, when political leaders promote national unity and emphasise mass mourning to the exclusion of almost anything else. After the killing of journalists at Charlie Hebdo magazine in Paris in 2015, some 40 world leaders walked through the streets in solidarity against terrorism. Such demonstrations are intended as a show of concern, but in practice they become a replacement for effective action.

Emotional outpourings, sincere or not, are politically convenient for governments because they divert attention from failed policies that may well have helped promote terrorist movements. Wallace is dismissive of “a foreign policy here, a foreign policy there” having any effect on terrorism, but the foreign policies most in question are those which led to Britain engaging in wars to overthrow Saddam Hussein in Iraq in 2003 and Muammar Gaddafi in Libya in 2011. Both wars succeeded in their aims, but they also led to a collapse of the Iraqi and Libyan states and opened the door to al-Qaeda, Isis and their clones.

It should be firmly said that, if Saddam and Gaddafi had not been overthrown, it is unlikely that Salman Abedi would have been in a position to slaughter people in Manchester.

There has been much controversy over Britain’s decision to join the invasion of Iraq, but not enough about its role in overthrowing Gaddafi eight years later. The nature of British participation in the Libyan war and the consequence of its actions deserve to be the subject of an inquiry as thorough as Chilcot’s. This is because the British participation went well beyond airstrikes and training of Libyan rebels. Reports are emerging that it involved energising and facilitating the movements of known Salafi-jihadi British Libyans and Libyan exiles who wished to return to Libya to fight Gaddafi. In other words, the Islamic jihadi networks of the type to which Salman Abedi and his family belonged acted as useful proxies for the British state.

Several Libyans in Britain had been subjected to “control orders”, a form of house arrest introduced after the bombings in London in 2005, to stop them going to fight in Iraq according to a detailed report in the online magazine Middle East Eye. Citing interviews with Libyan Islamic militants, it says that British authorities adopted an “open door” policy for Libyans willing to fight Gaddafi. “I was allowed to go, no questions asked,” said one source.

Other Libyans, with known Salafi jihadi associations, were surprised not only to have “control orders” lifted, but their passports returned. Many joined the Libyan Islamic Fighting Group when back in Libya. Belal Younis, a British Libyan, who had been to Libya in 2011, is quoted as saying that he was stopped by police and immigration officials on his return and then interviewed by an MI5 officer who asked him, “Are you willing to go into battle?” Younis says: “When I took time to find an answer he turned and told me the British government have no problem with people fighting against Gaddafi.” It had no problem then, but it certainly has a problem now as it investigates Libyans in Britain and Libya whom it once aided in pursuit of a foreign policy that destroyed Libya and became a danger to Britain.