The British Embassy is distributing iodine tablets as a contingency measure. Scientific advice is that the tablets should not be taken in the current situation.
You will be issued with sufficient stable iodine for two doses. There are detailed dosage instructions and other information in the package insert. There is also information about stable iodine on the Health Protection Agency website at: http://www.hpa.org.uk/Publications/Radiation/NPRBArchive/DocumentsOfTheNRPB/Absd1203
Tablets should be taken when: The UK Government advises to do so; the Japanese authorities advises people to do so; the Japanese authorities advise people to take shelter.」