I saw them whilst having my post-lunch tea. They were coming right towards our building, with the smoke still coming out, by the time I dodged outside, on the other side of the building, they had killed the smoke and were starting to turn more northward-westerly from their broadly westward flight over central London. I assume they were turning away from the Heathrow flight paths.
Quite impressive, but I wish I had known earlier, or I would have brought my SLR into work.
The Typhoons looked quite big, but I suspect that was more a reflection of how small the Hawks are!