Violation of Oslo accord discovered by MP who calls for action to investigate 'what other breaches are occurring' at the fair

The world's largest arms fair has thrown out two exhibitors after they were found to be promoting cluster munitions that have been banned by the UK and condemned by more than 100 other countries.

The organisers of the London exhibition said they had been unaware that the material was available and an investigation had been launched. But campaigners rounded on the Defence and Security Equipment International fair, saying it was "unbelievable" that more thorough checks had not been undertaken.

The action was taken after Caroline Lucas, the Green party leader, discovered that Pakistani arms manufacturers were actively promoting "banned cluster bombs" at their pavilions. Details of the munitions were in brochures readily available to potential customers.

A statement from DSEI confirmed that the two stands had been closed on Thursday evening. "(We) can confirm that the Pakistan Ordnance Factory stand and Pakistan's Defence Export Promotion Organisation pavilion have both been permanently shut down after promotional material was found … containing references to equipment, which after close examination, was found to breach UK government export controls and our own contractual requirements. [The] government fully supports the decision by DSEI to close the stand and the pavilion. We are currently investigating how this breach of our compliance system occurred."

Three years ago, the UK joined other signatories to the Oslo accord, which specifically prohibits "all use, stockpiling, production and transfer" of cluster weapons; they are considered particularly lethal because they are designed to release dozens, sometimes hundreds of "bomblets" on their targets.

They have been widely condemned because they have killed and injured hundreds of civilians long after conflicts have ended. One third of all such casualties are thought to have been children.

The episode is an embarrassment to the fair, which has had 1,300 firms from more than 40 countries seeking orders for weapons. Earlier this week, the defence secretary Liam Fox gave a speech there, saying that "defence and security exports play a key role in promoting our foreign policy objectives".

Lucas, the MP for Brighton Pavilion, has now written to Vince Cable, the business secretary, saying she remains "deeply concerned" at the level of scrutiny given to the companies who exhibit at DSEI, which has been running all week at the Excel centre in London's Docklands.

"I was able to find illegal advertising materials on the basis of one short visit to the exhibition with few resources at my disposal," she said. "There's no telling what other breaches are occurring and might be uncovered with further research." It should not be left to MPs and campaigners to police illegal promotion of banned arms on British soil.

Lucas said there is an "inherent conflict between the government's promotion of military exports and its stated desire to help protect human rights overseas."

Oliver Sprague, of Amnesty International, said: "It is almost unbelievable. It's not just cluster bombs, either. Earlier this week we found brochures (on different stands) which appear to show illegal torture equipment being advertised. It is quite amazing that it has taken a Green MP and Amnesty international to find things that are clearly illegal."

Kaye Stearman of the Campaign Against the Arms Trade, condemned the "laxness" that had allowed the companies to promote illegal equipment. "They should never have been allowed in," she added.

A spokesman for DSEI said it had no further comment. The Pakistan Ordnance Factory could not be reached for comment.

Earlier this week the Guardian reported that Pakistan was also advertising an "arms for peace" exhibition in Karachi next year as well as "gold-plated" submachine guns, "for collectors".