Britain was accused yesterday of dumping toxic household and industrial waste in developing countries on two continents in breach of an international convention.

The Government last night was considering tightening the enforcement of rules after the discovery of hazardous medical and electrical waste in Brazil and Ghana.

Hilary Benn, the Environment Secretary, ordered an investigation into two British companies linked to 90 shipping containers containing 1,400 tonnes of waste. They included syringes, condoms and nappies. The companies that received the waste - sent from Felixstowe to three Brazilian ports - said that they had been expecting recyclable plastic.

In a separate case, the Ministry of Defence was unable to explain how one of its computers was found by The Times on a notorious dump on the outskirts of Accra, Ghana. Children as young as 5 extract scrap metal from electrical items there and are exposed to potentially lethal chemicals.

Inspectors from Brazil's environment agency, Ibama, found hospital waste in several containers, reportedly including bags of blood. Another container was full of dirty toys with a note in Portuguese saying they should be washed before being given to "poor Brazilian children".

Ingrid Oberg, an Ibama official, who opened containers found in the port of Santos on national television news, said: "Whoever put this rubbish into the containers in the UK knew what they were doing and knew where they were going, so it is a criminal act. England needs to assume responsibility."

Roberto Messias, Ibama's president, said: "We will ask for the repatriation of this garbage. Clearly, Brazil is not a big rubbish dump of the world." The agency said that it was considering taking action against two British companies it believed were connected to yesterday's find - Worldwide Biorecyclables Ltd and UK Multiplas Recycling Ltd.

Mr Benn admitted that there could be weaknesses in the enforcement of rules on sending waste overseas, including a European directive banning the export of any electrical waste. Speaking to The Times about the discoveries in Brazil, he said: "If, having looked into this particular case, there are lessons that need to be learnt about enforcement, then we will do that."