They are Boots-branded Micropur tablets, from a local (UK) chemist. I am fairly sure they are made by Katadyn. ETS shows a similar product in the Water and Food Group page but they are not identical. The ETS ones are in foil but are much bigger than mine. Mine are in strips that look like the ones near the bottom of the Katadyn page. Also, the ETS page says the active ingredient is chlorine dioxide and the Boots ones use silver.