Minor Indian Passport Renewal

[RajTPT]

Hi,

I'm in the process of applying for my Son's Indian passport renewal. I hold British Passport and my wife holds Indian passport.

Below is one of the documents required in my case:

"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 required"

I'm not sure who is the concerned UK authority I should contact for this letter and how.

Your advise would be much appreciated

Thanks
Raj