Thanks CR001. I appreciate your help on this.

I will keep 1.9 blank. Does it need an explanation in the "further information ... " page?

@CR001

Should I use form MN1? If yes, then what should I write in item 1.9 (MN1) - Present Nationality?

My son was born in UK in September 2018. At that time I was in Tier 2 (General) visa. In October 2018 I applied for Indefinite Leave to Remain (ILR) in UK and received it. As per UK rule my son is now eligible to apply for a British citizenship as one parent acquired ILR after his birth. I did a ...