The waste included used nappies, syringes, used condoms, batteries, food remains, used packages of cleaning products and cloth, according to Brazilian news reports and images taken during an inspection by Ibama, Brazil's environmental agency.
A spokesman for Britain's environment agency said: "Where the environment agency detects or is made aware of the illegal export of waste, it works with all relevant partner authorities to ensure the environmentally sound management of any illegal shipments - including the possible return of wastes to the UK.
"If any company is found to have contravened the strict controls on the export of waste as set out by the Basel Convention, the Environment Agency will not hesitate to take enforcement action."
The United Nations-administered Basel Convention, which came into force in 1992, bans shipments of toxic waste from industrialised countries.
The rubbish, which has been linked to two British companies, was sent from Felixstowe in eastern England to docks at Brazil's Santos, near Sao Paulo, and two other ports in the southern state of Rio Grande do Sul, Britain's Independent newspaper said.
The companies in Brazil that received the waste claimed to have been expecting recyclable plastic, said The Times, another UK newspaper.
"I'm surprised to learn that trash was improperly imported, with a false characterisation, from Britain into Brazil," Roberto Messias Franco, Brazil's state environmental agency chief, said in a statement on Friday.
"Brazil is not the world's dump," he said