At what point was the intercept made, does anyone know? The Flightradar track shows the Antonov trundling up to Heathrow at 18,000ft, then making a sharp right turn.
How could the pilots possibly have ended up that close to Heathrow without realising they'd missed a few conversations with ATC?
And what on earth would the Typhoons have done if it had looked like the An was planning something hostile? Shoot it down over Lambeth or Hounslow?