This actually happened to me 2 nights ago whilst squeezing the proverbial quart into a pint pot that is the 0600-0700 hour at EGLL. The scene - me trying to get them as close as possible using 27L & 27R and I thought I'd better tell a BA 747 on 27L that he was closing "slightly"
on an SAA 747 on 27R
Me - "BAW***, you may see traffic in your 1 o'clock, range 2.5 miles, a Springbok 747 established on 27R"
BAW*** "Oh yes, we have it in sight - we thought it was OUR strobes!" :o