A British regency normally follows the succession before seeking a guardian

How would a British regency have worked in the early twentieth century?

The next senior prince would normally act as regent, with a suitable senior lord or royal uncle considered for an infant regency.

The ordinary rule makes the senior prince next in line to the throne regent. An infant regency creates an additional problem because someone of suitable character must exercise authority. That figure might be a powerful senior lord or an uncle within the royal family. Regency extends succession principles while accounting for the age and capacity of the available heir.