A few years ago, I was talking at length to a former Concorde SFO who took me through the entire "Swiss cheese" scenario. He stated that the source of the ignition was not the afterburners as I had presumed. The ignition source was (at that time) believed to have been in the wheel well, possibly through an electrical short.
Has this been disproven or is it still believed to be the case ?
I asked by how much in relative terms was the aircraft overweight. I think the answer was around 4% based on what had been officially recorded.