Sushi
kyoto gardens holland park
fan museum greenwich not specifically japanese butI beleivethey have a japanese collection and they would probably do a group tour aimed at Japanese fans if you asked then either lunch there or somewhere local
Brunei gallery they have japanese garden on fourth floor, The Roof Garden is available for hire for private functions
Peace pagoda in battersea park but can't think ofacrporte angle...
dinner and sake tasting at japanese society
Kimono fashion show and dinner
Is that enough for now?