Melmothtw, as I say read the linked leaflet.
”(e) A “British citizen otherwise than by descent” is someone who can pass their citizenship onto a child born overseas. Generally speaking a British citizen otherwise than by descent is a British citizen who was born, adopted, naturalised or, in most cases, registered in the United Kingdom or a qualifying territory.
(f) A “British citizen by descent” cannot normally pass on citizenship to a child born overseas. A British citizen by descent could have become such a citizen in a number of ways – for example: by birth outside the United Kingdom to a parent who was a British citizen otherwise than by descent........
4. CHILDREN WHO ARE BORN OUTSIDE THE UNITED KINGDOM TO BRITISH CITIZENS BY DESCENT
A child born outside the United Kingdom will not be a British citizen if neither parent is a British citizen otherwise than by descent. A parent who is a British citizen by descent cannot normally pass that status on. The exception to this is where the parent was in one of the 3 types of service listed in section 5 at the time of the birth.......