United Kingdom - Passport & Nationality - British Citizenship by Marriage (Pre 49)
A woman married to a British Man (by birth, descent or otherwise) before 01.01.1949 becomes British automatically on 01.01.1949, irrespective of what nationality she held or where she was born.
An unintended consequence of the recent anti-gender discrimination legislation passed recently means that any children born to this women - even from a subsequent marriage - may have a claim to British Nationality in the modern day.
Watch this SHORT VIDEO by Mishal Patel and Philip Gamble on the theory and how this solution arises: