Anybody know what the movie was called with (i think)dennis waterman, where he falls in love with a mannequin?

only he can see it move, i think he ends up in a mental institute at the end, and the mannequin on a rubbish tip, where somebody else finds it and they can see it move too. i think it was made early seventies?, but can't see it on imdb.com. any useful answers would be most grateful for, thanks.