Not sure if this is a British film, just know the children spoke with a British accent, but perhaps someone will remember anyway. I saw this film on late night TV in the late 60's. Two children were wealthy and lived in a town on the sea/ocean in what could have been Italy. They were brother & sister or cousins or related in some way, and they got into a relationship that they shouldn't have (could have been just kissing, I'm not sure). Somehow one of them drowned, either by being pushed or just falling from a boat dock or pier. I tend to think pushed, because other one lied about what happened. It had a lot of boats - esp. sailboats - in it, and a lot of scenes by the water. Does anyone remember this film?