Just listening to the official soundtrack of the opening theme to A Grand Day Out, the speed/pitch matches that of the Blu-ray, so wouldn’t that mean the Blu runs at the correct speed?
Was the soundtrack ever offically released?
I did a search for the soundtrack on YouTube myself and found this;
In the description, the uploader said he had to speed the audio up (from a source uploaded previously by another user) by 4% to make it accurate. Maybe that link you found was sourced directly from one of the 24fps Blu Ray audio?