Japan’s nuclear safety agency raised the severity rating of the crisis at its nuclear plant to the highest level today, on a par with the 1986 Chernobyl disaster.

Seawater outside the crippled nuclear power plant in north-eastern Japan was found to contain 3,335 times the usual amount of radioactive iodine – the highest rate yet and a sign that more contaminated water was making its way into the ocean, officials said today.

Japan has promised to overhaul nuclear safety standards once it regains control of the wrecked Fukushima complex, admitting its current safeguards were not enough.