Water that the Japanese government is planning to release into the Pacific Ocean from the crippled Fukushima Dai-Ichi nuclear plant contains radioactive material well above legally permitted levels, according to the plant’s operator and documents seen by The Telegraph.

The government is running out of space to store contaminated water that has come into contact with fuel that escaped from three nuclear reactors after the plant was destroyed in the March 2011 earthquake and tsunami that struck north-east Japan.

Its plan to release the approximately 1.09 million tons of water currently stored in 900 tanks into the Pacific has triggered a fierce backlash from local residents and environmental organisations, as well as groups in South Korea and Taiwan fearful that radioactivity from the second-worst nuclear disaster in history might wash up on their shores.

Tokyo Electric Power Co., (Tepco) which runs the plant, has until recently claimed that the only significant contaminant in the water is safe levels of tritium, which can be found in small amounts in drinking water, but is dangerous in large amounts.

The government has promised that all other radioactive material is being reduced to “non-detect” levels by the sophisticated Advanced Liquid Processing System (ALPS) operated by the nuclear arm of Hitachi Ltd.