Britain's military operations since the end of the cold war have cost £34.7bn and a further £30bn may have to be spent on long-term veteran care, according to an authoritative study.

The bulk of the money has been spent on interventions in Iraq and Afghanistan judged to have been "strategic failures", says the study, Wars in Peace, published by the Royal United Services Institute (RUSI).

In comments with particular resonance in the light of Tony Blair's speech on Wednesday exhorting the west to do more to defeat Islamic extremism, the RUSI study concludes that "there is no longer any serious disagreement" that Britain's role in the Iraq war served to channel and increase the radicalisation of young Muslims in the UK.

The RUSI study refers to estimates of 100,000 Iraqis killed, with 2 million refugees fleeing to neighbouring countries.

Most of the study's figures have been collated for the first time from responses to freedom of information requests to the Ministry of Defence. If the material cost of British deaths and injuries in subsequent compensation payments is included, the cost to Britain of military conflicts since 1990 could total as much as £42bn – excluding the cost of caring for veterans.

What the study describes as "largely discretionary" operations – the failed interventions in Iraq from 2003, and in Afghanistan after 2005 – accounted for 84% of the total cost of British military interventions since 1990.

The figures are net additional costs of the operations – that is, on top of what the armed forces would have been spending in any case, on running costs such as fuel, training exercises, and salaries.

In what it calls a "strategic scorecard", the study gives UK military interventions six out of 10. Counted as the six successful operations are the first Iraq war in 1991, later no-fly zones over Iraq, the later interventions in Bosnia, the Kosovo war in 1999, Sierra Leone in 2000, and operations launched in 2001 which led to the flight of the Taliban and al-Qaida leadership from Afghanistan.

Failures are listed as attempts at peacekeeping in Bosnia in the early 1990s, the 2003 invasion of Iraq and its aftermath, the British deployment in Helmand in southern Afghanistan, which started in 2006, and the air strikes in Libya in 2011.

RUSI says "there is no longer any serious disagreement" over how the UK's role in the Iraq war helped to increase the radicalisation of young Muslims in Britain. "Far from reducing international terrorism … the 2003 invasion [of Iraq] had the effect of promoting it," the study concludes.

"The rise of Al-Qaida in the Arabian Peninsula (AQAP) was a reaction to this invasion, and to the consequent marginalisation of Iraq's Sunni population (including de-Ba'athification and army disbandment).

"Today, AQAP and other radical jihadist groups stretching across the Iraqi-Syrian border, pose new terrorist threats to the UK and its allies that might not have existed, at least in this form, had Saddam remained in power."

The study says that, although Saddam Hussein was one of the most brutal dictators of the late 20th century, responsible for successive atrocities against his own people and wars of aggression against his neighbours, by 2002 "the scale of these misdeeds had been much reduced, not least because of the containment measures put in place after 1991".

Last year's parliamentary vote in Britain opposing intervention in Syria took place "in the shadow of Iraq", the RUSI study says.

Britain's intervention in Helmand, notes RUSI's research director, Malcolm Chalmers, began with its decision to insist on the decision to dismiss the governor, Sher Mohammad Akhundzada, driving many members of his forces to join the burgeoning militia. Meanwhile, Taliban foot soldiers confronting British troops in Helmand were primarily recruited locally, "motivated much more by opposition to foreign intervention than by global jihadism".

The study notes that opium cultivation is higher today than it was before the British arrived. Britain was assigned special responsibility for countering narcotics in Afghanistan on Blair's initiative in 2001.

In an earlier attempt at auditing, Frank Ledwidge, author of Investment in Blood, published a year ago by Yale University Press, estimated that by 2020, Britain will have spent at least £40bn on its Afghan campaign – enough, he said, to equip the navy with an up-to-date aircraft carrier group or recruit and equip three army or marine brigades and fund them for 10 years.

RUSI considers the potential savings but also potential cost of not participating in the military operations, including abandoning Britain's position as Europe's "most capable military power".