Me again!
A tiny little longhaired tabby (with a collar) has started to come through our flap and eat Jamesons food - mainly around the same times in the mornings, but possibly during the days too, while we're out. She (or he) meows very loudly - almost cries, but as soon as I hear the flap and goes to check, she'll hurry out through the flap and sit outside and meow. She seems timid but has a collar so must be owned by someone?
Sometimes Jameson will come in and spend ages sniffing the walls in the kitchen area and around the house - a sign the cat has been indoors.
What is the best thing to do to prevent her from coming in? I locked the flap but had to unlock it before going out so J could come and go, but OH went outside and shooed her away. Getting a microchip/infrared flap is the last resort - are there other ways to 'teach' a cat not to come in???