I had to answer a very similar question recently. I (and those I consulted) concluded that, going back to basics, an instrument approach is complete on acquisition of the required visual references. The landing is then completed visually. All Cat1 Instrument approaches become visual approaches at some point without further approval from ATC.
Therefore, all that stuff about whether or not you need permission, or 800m, or anything else, is obscuration. You were on an instrument approach - you acquired the visual references - you used them to land. End of story.
Last edited by keithl; 31st Jan 2008 at 13:38.