I've just spotted Epsom hiding at the bottom of this...
Taking the LAT/LONG off that as 51.20N 000.17W puts it just east of my previous plots (pink pin) so I think we can safely say it has moved.
As to when it moved, I think we can assume that it was in its original position when Lord Trefgarne asked his question in Feb 1968 and the co-ordinates provided by Discorde from Nov 1969 has it in the current position (allowing for datum change) so sometime in that window.