Indian passport renewal for minor father British mother FLRM

Hi Please help Gurus
I have to apply for my child's indian passport renewal, I recently became British citizen however my wife and son are still indian nationals and they are on FLR M visa UK. dependents of settled person.
when I was looking on VFS website for required documents I came across with below paragraph.

If either of the parents holds a foreign nationality, then a letter from the concerned Embassy or Mission of that country or from the concerned UK authority (in case of British national) stating that the child has not acquired nationality of his / her parent would be[/u] required.[/u]

can you please advise me what kind of document you are requesting from home office uk, I called them they said they don't issue any letters for individuals.

Kindly help me with this query.

Application for proof that you do not have British citizenship: form NQ

UKV&I fees

The fee for a Form NQ letter is £198.

Thanks a lot Simon.