The manual says "lift off" ha ha. After a half hour struggle, I slid a thin knife round the edge and eventually, using a screwdriver carefully twisting it in the centre hole, managed to get it off. The reason? The instruction label on the edge of the filter (a copy of the manual's instructions on washing the filter) had stuck to the grey outer filter holder. It's out with the sandpaper whilst I now wait 12hrs for the filter to dry.
harry d, Poole, September 2009