I've always been told he was portuguese. But there are several countries claiming he was their citizen. But he was most likely Portuguese , spanish or italian.
Never heard of the british theory ...
Arguments used by proponents of the Portuguese hypothesis is that in a court a document mentioning Columbus nationality, they called him "portuguese" and in another Columbus uses the word "homeland" in relation to Portugal.
And a book by Alfredo F. De Melo of Uruguay credits Dr. Manuel L. da Silva, MD., of Bristol, R.I.,for a series of literary discoveries.
Dr.da Silva and his wife, Silvia, went to Vatican in July 1994 to investigate the papal bulls relating to the New World discoveries.
They made some discoveries supporting the theory that Columbus was Portuguese. They found two papal bulls dated May 4, 1493, written in Latin by Pop Alexander V1 referring to the discoveries of the Western Hemisphere by Crisrofõm Colon.
Dr da Silva points out that the name is written in Portuguese and not Spanish (Cristobal Colon), is not written in Latin like the rest of the manuscript (Christopher Columbus), and is not written in Italian (Cristoforo Colombo.)
Dr da Silva added, "Cristofõm does not have the "h", and the till ( ~ ) over the o is used only in the Portuguese language."