Hi, Regarding the Islander you saw, it could possibly be one of the “specials” that operate out of Northolt. Both G-BIIO and G-BSAH have been out and about over the past week on a regular basis……neither show up on tracking sites! The only doubt I have about it being one of those, is the fact the one you saw was at “low level”.
With regard to the A400 that routed south, this was carrying equipment etc, in support of the Red Arrows who left Scampton yesterday for training in “sunnier climes”
Regarding some interesting aircraft operating over London, there are Aussie C-17s airlifting “equipment” eastbound via Brize. Also there is a New Zealand Herk in Brize for the next two months, which is also helping out with the same airlift!