Scores of Iraqi civilians were killed or injured needlessly, because Britain failed in its duty as an occupying power, a human rights group claims.
Cluster bombs are blamed for causing civilian casualties
Its use of cluster bombs and failure to secure Iraqi munitions dumps have been criticised by Human Rights Watch.
Their report says coalition forces tried to avoid killing civilians, but hundreds of deaths were preventable.
It also criticised Iraqi forces for using human shields, landmines and Red Cross and Red Crescent symbols.
Researchers were sent to Iraq between 29 April and 1 June to look at civilian casualties and the damage to infrastructure.
The Ministry of Defence (MoD) says that in tests, only 1% of its cluster bombs failed to explode.
But researchers reported finding "multiple unexploded British sub-munitions" in the Tannuma area of Basra, in southern Iraq - including three in one garden.
And they said thousands of tonnes of unsecured Iraqi munitions were found in the British-controlled sector - risking lives and providing anti-coalition forces with weapons.
"Children playing in, and civilians scavenging through, the sprawling weapons caches often set off explosions that caused death or gruesome injuries," the group said.
But the report found coalition air forces had learned lessons from past wars and dropped fewer cluster bombs in populated areas, reducing casualties through better targeting and technology.
The findings prompted calls from the Liberal Democrats to ban the use of cluster bombs and amend the Landmines Act.
The prime minister's spokesman said on Friday he was not aware of any plans to review the use of cluster bombs.
The MoD said it supports their use against legitimate military targets in order to protect British troops and civilians from further harm.
It says care was taken to avoid populated areas and to limit risks to civilians, but it was impossible to rule out casualties.
Along with the UN and other organisations the MoD is clearing munitions from Basra, many of which it says were there before the conflict started.
But in its own report it said a contract has only just been awarded to an American company to deal with 50 ammunition dumps.
"We are in the process of clearing up these weapons, it's going to take some time, a lot of weapons were distributed around the country before [the war]," said an MoD spokesman.
"They are not all cluster bombs and they are not all coalition weapons."
Officials have also been advising schools and community leaders about the dangers of munitions dumps and unexploded weapons.