That email from Oxford Union spelled the word "Organisation" as "Organization".

I think it's safe to say that the Pinkos have infiltrated Oxford and it is therefore no longer able to be considered any authority on the observable universe.

Carl should get a Subject Access Request (SAR) on every document they have which refers to him in their records. This decision to have him no longer invited will have had to be signed off by someone and that someone is accountable for said decision - what other decisions do they make?

As it is his personal information he'll have to request it himself, but that shouldn't cause any issue as they would no doubt have had background checks done on an invited guest to their property to deliver a talk. This will show up in the SAR.

Their failure to comply with his request will force the Information Commissioner Office to audit their processes and lay down a fine and actions required for future continuance of being the entity that they claim to be.

The great thing about this is that it will cost Carl no more than some of his time in writing the request and supplying identification to prove that it is his own information that he is requesting.

I imagine whoever penned that email might learn to spell properly with the King's English in future correspondence (As well as understand law).