That's quite a statement. How would you know that? A presumption, based on far far less than the info re: his parents marriage (which isn't a whole lot).
The marriage may have taken place in Maui. The marriage may have taken place in Africa. The marriage may have taken place elsewhere, or may not have taken place at all. Like most everything else with Barry, we don't know a whole lot.
What we do know, is that there is a court record regarding the divorce.
Until there is actual proof to the contrary, it would be a prudent legal challenge to his eligibility to use his own public admissions of being "governed" at birth by a foreign power, against him (IMO).
You are just beginning because apparently you have no idea that it is likely that he was not a British citizen. Unless you are leaving that point out on purpose in order to misinform people.
Go with the divorce papers.
If true, he very likely was not a British citizen. You could try to use his own admission against him..but it still doesn’t make him a British Citizen. He can proclaim he was a British citizen all day long..it doesn’t make him one.