Uk passport application for non EU citizen. Which is best way to go?

[StrawberryShortcake32]

I'd appreciate some help from my fellow mumsnetters please.
My husband immigrated to the UK 12 years ago from South Africa. We've been together for 6 years and married for 3.
Both sets of his grandparents were British who immigrated to South Africa and this was the reason his indefinite leave to remain was approved.

My question is, which is the best way for him to apply for a UK passport?

1. Using his ancestral roots
2. Married to a UK citizens

Is there one that's easier, quicker or cheaper than the other? Or can he use both?

I've tried ringing the passport office but they don't seem to understand what information I'm asking them.

If anyone has any insights I'd be really grateful

I think from looking at the gov.uk website he qualifies based solely on having lived here for that length of time and having indefinite leave to remain. Being married to you and indeed his ancestry doesn't actually need to be a factor.

He doesn't meet the requirements for registration so naturalisation is the route available.

He needs to naturalise as a British Citizen before applying for a passport.
I had an ancestry visa and then ILR before naturalising,it was very straight forward.
He cannot just apply for a passport beford this step. HTH

In the naturalisation application, he can list all relevant criteria, OP. May as well, won't hurt. Does South Africa let him be dual citizen?