@tomahawk_PA38
Here's a chart of
AF Concorde routings:
Concorde route
Given that BA and AF used the same "Sierra November/Sierra Oscar" EB oceanic routes, and Paris and London are about the same longitude, the decel point was likely nearly identical as well.
Handwritten note is a bit small, but I believe it amounts to "50nm east of BISKI."
Waypoints change, however, and BISKI no longer exists - the closest approximation to the actual decel point that I see on a
current chart looks like it would be MOSIS. Mouth of the English Channel, just west of the Scilly-Ushant line.
Deceleration clear of land then takes you directly up the center of the channel to SSW of Southhampton (roughly, ORTAC), and then hang a subsonic left to Heathrow.
But I'd also love to hear if someone has more authoritative info.