"Just a thought.
How often does AAIB release preliminary findings in less than a fortnight?"
In the old days they never used to release preliminary reports, but they started doing it in the last decade or so.
They tend to do it with any high profile or high interest incident or where they discover a serious issue that may affect airworthiness on a type.....the 777 at Heathrow had a number of preliminary reports as did the spate of puma incidents in the north sea. There have been quite a few other instances of preliminary reports too.
Here's a list of them
Air Accidents Investigation: Special bulletins