I'm certainly not saying 'kitchen porter' is wrong, but if you click http://www.acronymfinder.com/af-query.asp?String=e xact&Acronym=KP&Find=Find
a link will take you to the acronymfinder web-page that lists 23 possible meanings for 'KP'. The only one that seems to deal with kitchens does, indeed, say it's 'kitchen patrol'.