Tony Blair is facing fresh fury over the use of controversial munitions in the Iraq war. Campaigners lambasted the Ministry of Defence over its use of deadly cluster bombs and shells during the invasion, warning that they could contravene international law.

MPs are to table a raft of new questions today over the affair amid fears that thousands of bomblets released during the war will leave a deadly legacy for Iraqi civilians. They warned that any unexploded bomblets could kill or maim civilians for years to come.

The dispute over British use of cluster bombs will be intensify this week with the publication of a report by the pressure group Landmine Action, which raises questions over the efforts made to ensure that the weapons did not harm civilians. It comes as international signatories to the international convention on conventional weapons meet in Geneva this week, amid pressure for a moratorium on the production of cluster bombs and tough new limits on their use.

The report, funded by the Diana, Princess of Wales Memorial Fund, said British officials had failed to gather field data about the failure rates of cluster bomblets, and had done "little or nothing to gauge the humanitarian impact of these weapons".

It said that the UK had "failed to undertake any significant effort to understand better the impact of cluster munition use and has continued to use them. As was foreseeable, these cluster munitions have been a cause of civilian casualties."

Michael Moore, the Liberal Democrat defence spokesman, said: "This is a very significant report which raises some very serious issues. There is clearly a lack of information and I will be tabling questions and writing to the Secretary of State with a copy of this report seeking detailed answers to the questions it raises. The jury may be out on the political legacy of the coalition's time in Iraq but the military legacy could be absolutely devastating."

Jeremy Corbyn, the Labour MP for Islington North, also said he would raise fresh questions about the affair. He said: "My concerns about the issue of cluster bombs are as strong as they ever were. Unexploded bomblets lying around can be picked up by farmers and children in the community and can be lethal. They can be buried and can be as bad as land mines."

A report published in 2003 by the group Human Rights Watch said British forces had killed dozens of civilians in and around Basra using ground launched cluster munitions.

Britain confirmed in 2003 that it dropped substantial numbers of cluster bombs during the campaign. The Ministry of Defence said that 2,000 bomblet shells were fired by artillery on the ground and 68 cluster bombs were dropped from the air during the war.

Ministers insisted that the weapons were targeting "specific military targets", but later confirmed that British troops used cluster bombs in built up areas. The revelation sparked a storm of protest after The Independent revealed in 2003 that Adam Ingram, the Armed Forces minister, had admitted that the use of cluster bombs against civilian targets would not be legal.

Parliamentary written answers released at the time also confirmed that the MoD had carried out no reviews or assessments of the civilian casualties caused by unexploded bomblets used in the Gulf region, Kosovo or Afghanistan. The Ministry insisted last year that it had cleared more than one million unexploded bombs in southern Iraq, including 6,000 sub-munitions, or bomblets.

Ministers insist that the cluster bombs are not indiscriminate and represent an acceptable "balance between the threat to civilians and the need to protect British forces". But critics said the answer provided too little detail to determine whether British forces had removed all threats to Iraqi civilians.

The Landmine Action report also warned yesterday that the bomblets could have a 10 per cent failure rate, and said that in conflict zones such as Kosovo unexploded munitions were still being found years after the end of hostilities.

It said a British Government report had acknowledged that airborne cluster bombs had an "unacceptable" failure rate, and warned: "It is far from clear that those making decisions about the use of cluster munitions routinely do so or even could do so with a serious sense of the possible effects of the weapons."

Simon Conway, the acting director of Landmine Action, said: "These weapons were designed for use against columns of vehicles on the German plains. If you fire an artillery shell into a populated area fighting irregular troops like in 2003 and you use a weapons system like this in that context it can be indiscriminate."

A spokesman for the MoD insisted: "Cluster munitions are entirely lawful weapons. If we did not use them we would have to use something much more hazardous to civilians."