Yes, it was quite a treat. Their apparent brightness was too similar for this observer to decide which was which. (Anyone else able to decide? The ISS should be brighter than Discovery, being much bigger.)
The angular separation, as seen from my position, was of the order of 2 degrees, and seemed steady. (Just over the width of a finger at arm's length.) This leads me to speculate that Discovery may have positioned itself at the same orbit altitude as the ISS, either leading it or following it. (A lower orbit would be faster; higher orbit slower.)
When abeam us, they were over the north coast of Spain, so about 500nm (nautical miles) from SE England. Off the top of my head, 2-degree separation would equate to a separation of just over 15nm, i.e., about 30km.