Terence Meaden is correct in saying that the outlying stone (at Winterbourne Bassett) is a modern addition. It was found in the south-west field and then erected on the corner of that field some ten years ago. I vaguely remember seeing it shortly after it went up and know someone involved with its erection. The stone was still pinkish in colour then (perhaps suggesting that it had never been above ground nor had ever formed part of any megalithic structure).