British by decent

[Sw1108]

Hi
I wonder if you could advice me on a situation. My husband is a Jamaica national born in Jamaica, his father is born british born in 1958.
His father then retuned back to Jamaica in 1959 with his parent which made him 1 years old at the time so he was on his father passport.
He has lived in Jamaica ever since and has never returned to England.
So that would make my husband british by decent because his father is British other than by decent.
My husband has now applied for a british passport based on that his dad is british the only problem is his parents wasn't married so he has based his application on the fact that his father domiciled in Jamaica.
And Jamaica see him as a ligitamate child.
He submitted his father full uk birth certificate also his father british passport.
He also submitted his grandfather passport that his father came over to Jamaica as a baby, he also got a reference from his father workplace where he has worked for the last 16 years.
He was called for a interview last week and was asked to bring some document with him which included a domicile questionnaire. The interview went ok he just waiting now.
What do you think the out come for this application will be?
And do you know anyone who has got british passport by british by decent?
And do you know how long the process is?
Awaiting your reply.

Many thanks