The UK food watchdog has launched a fierce defence against criticism over its claim last week that organic food gives consumers no extra health benefits.

In a surprising move, Tim Smith, chief executive of The Food Standards Agency (FSA) wrote an open letter to back the review, commissioned by the watchdog, which found organic food had no "additional health benefits".

"The important message from this report is not that people should avoid organic food but that they should eat a healthy balanced diet and, in terms of nutrition, it doesn't matter if this is made up of organic or conventionally produced food," Smith said.

The study has drawn criticism from supporters of organic food, some of whom claimed the review rejected key research that had compared organic and conventional food in the past.

Smith, however, said the FSA has "complete confidence in the validity" of the review.

He added: "Irresponsible interpretation of the review by some has resulted in misleading claims being made concerning higher levels of some nutrients found in organic food."