I think you'll find that the second "BA 777" waiting for departure was actually a 767 (I was flying it!). We were not actually lined up, but were negotiating the S-bend chicane on the South side of 09R.
From what we heard the Saudi 777 was about to line up when he reported a "box" in front of him that looked like it belonged on an aircraft. Then one of the Midlands chimed in, saying he could see debris on the runway - excellent spot as I couldn't see anything. 09R was closed for about half an hour and, listening to delivery, the delays it caused were quite substantial. Some aircraft were allowed to depart from 09L, but only a few got away before 09R reopened.
Hope this is of interest.