British Passport application processing Query

Please can someone help answer my question regarding the supporting documents for British passport application:

On the government website it says:
You’ll need both:
- your naturalisation or registration certificate
- the passport you used to come into the UK or the foreign passport you’re included on

The passport I used to enter into the UK - does this mean the passport that I used to first ever enter the UK? Or my current passport that I use to enter the UK?

It’s very confusing and I’m a bit concerned because I couldn’t find my old passport that I used to first ever enter the UK.

Did anyone else have the same issue? Or did you only send them the current passport?

Thank you!

A common scenario!

Passport you first entered UK with means the FIRST not the current, which of course you have to submit as well.

You can’t provide what you don’t have.
It is not a requirement of the process to produce that passport. You should just explain why you can’t provide, add a covering note. Maybe you have a copy of it? You could attach that as well0

The reason HMPO ask for foreign passports is that they want to ensure that all travel documents show the same name. They don’t want citizens using multiple identities.