By David Loyn
BBC World Affairs correspondent
The UK government has been accused of trying to reclassify two kinds of cluster bombs so they can still be used after a proposed global ban begins.
Cluster bombs were used in Iraq
Landmine Action said the government wanted to make use of its current stocks of the controversial bombs which open up to scatter smaller bombs.
The government says its position was backed by the International Committee of the Red Cross (ICRC).
However the ICRC says this has never been discussed with them by Britain.
This comes as three churches in Britain call for a complete ban on the use of "indiscriminate" and "terrible" cluster bombs by UK forces.
In a joint statement, the Baptist Union of Great Britain, the Methodist Church and the United Reform Church also pressed Foreign Secretary David Miliband to actively support an international treaty to ban such weapons.
Moral high ground
The campaign group Landmine Action says the government's position calls into question Britain's desire to hold the moral high ground on this issue, claimed in March when it announced it was the first major power to scrap cluster bombs voluntarily.
There is an international consensus growing around the idea of banning cluster bombs.
These have been particularly harmful to children in the Balkans as well as Afghanistan and Iraq, because they tend to pick them up after conflicts, setting off the explosion.
A ban is being considered through the CCW (conventional weapons) negotiations at the UN, as well as the separate Oslo process.
As the serious negotiations begin this winter, Landmine Action questions why Britain is trying to hold on to two kinds of munitions.
As recently as last November, an air-launched rocket, the CR7/M261, was included in a list of cluster bombs issued by the Ministry of Defence.
But in a parliamentary answer in July, Defence Minister Bob Ainsworth said this "does not fall within the UK's understanding of a cluster munition".
The reasons given were firstly that it is "directly" fired, in that it can be targeted accurately, and secondly that it has too few sub-munitions, or "bomblets", to use a less technical word.
Simon Conway, director of Landmine Action, says if this was a cluster bomb last November, then it still is.
Neither of the government's points are internationally accepted definitions that would exclude this rocket from a ban.
With 19 rockets carried in each pod, and two pods to a helicopter, one strike could deliver more than 340 bomblets.
Mr Conway said: "It's a con. I think it's an attempt to try to secure a short-term advantage.
"Because we have got these things on the shelf we want to hold onto them, and that is very damaging. It has all the characteristics of a cluster munition.
"It's delivered by rocket as many are. The rocket breaks open in the air, and large numbers of these small sub-munitions fall down out of the air and saturate an area that might cover several football fields.'
The Ministry of Defence said: "The UK is committed to improving reliability of all munitions, including cluster munitions, with the aim of achieving lower failure rates and leaving less unexploded ordnance."
A spokesman said there was no international agreement as to what constitutes a cluster munition, and as Britain's assessment had evolved, so it had concluded that the CRV7/M261 "should not be classed as cluster munitions".
This view was also currently shared by the International Committee of the Red Cross (ICRC), it said.
But Peter Herby, the head of the arms/mines unit at the ICRC, one of the most widely respected organisations in the world, said the ICRC had never discussed this issue with Britain.
He said the ICRC was not the arbiter of the definition of cluster munitions, now the subject of international negotiations.
The other cluster bomb that Britain wants to keep in its arsenal is the M85.
The government argues this is a "smart" cluster bomb, because it has a self-destruct mechanism if the initial trigger fails to work.
But Landmine Action says the self-destruct mechanism too often fails.
The ground of southern Lebanon is littered with unexploded M85 bomblets, dropped by Israel last year.
Simon Conway says: "The UK government is claiming that if you put a self-destruct on, then that makes it smart. No-one else is saying that.
"This is basically the UK government trying to keep hold of a few of the weapons systems that it's got by playing fast and free with definitions.'
Research by Landmine Action even suggests the auto-destruct system can make these bomblets more unsafe, because it provides an extra trigger to detonate the device if it is picked up.
Ten years ago today, in the weeks after the death of anti-mine campaigner Princess Diana, the international deal to ban anti-personnel mines was agreed in Oslo.
Campaigners demanding momentum now on the road to ban cluster bombs fear the signal sent from Britain will weaken international resolve on this issue.