Does anybody know?
The fact that it says Best Before, means that it's not best quality afterwards, but should still be able to be consumed.
What would you think happens after the BB date? Could it get even more sour, which would then be an improvement in the quality as it was sourness that was needed! Or do you, perhaps, think that the sourness goes and you end up with normal cream?
Or do you have any other ideas, including, (within reason), what you would do with it.
(This isn't meant to be a scientific discussion, just a little light hearted chat).