I can confirm the same, saw it too. The loud sound of the engines approaching made me wonder if there was about to be a ......., but the 747 flew over, banked, lowered it's undercarriage and seemed to be joining 27L without further incident. I thought that it was a ferry from LGW to LHR to be honest, but nevertheless it gave me a fright, we're not used to them that low in these gentle parts.
SHJ