Gentlemen
May I just point out that RAF claimed a total of 37* or 46** He 111 as destroyed on this day, many over and near Belgium. Many more were claimed as damaged and some further are listed as "destroyed unconfirmed", which later would be listed under the nomenclature
probables!
I ALSO suppose it is more relevant to say the French CLAIMED 18 He 111 shot down that day!
I doubt if it will be at all possible to determine (when counting the true number of lost He 111) how many were shot down by which Air Force.
However RAF was based more to the north in France and many of their combats took place over or near the Low Countries, which at least to me indicate that many if not most of those were destroyed by the RAF!
We do have an author who appears rather regularly on TOCH who HAS done research on this day (and another 11 one's

), so I suppose he has a lot more to say about this than I do
Cheers
Stig
* Twelve days in May
** RAF Fighter Command Victory claims vol 1