Thanks for the update

Which helpline did you contact?
I tried yesterday to call the home office and the lady did not have a clue on what that letter was...

That is exactly what I have received yesterday.
I am thinking to send all the original documents, I will keep the original passport and attach a cover letter explaining why I did not send it.

Did you get more information regarding this?

It is the same list that will be given to you at the end of the online application. 'SAME LIST OF DOCUMENTS YOU CAN FIND AFTER THE APPLICATION' means that on the letter received by the HO is written exactly what was in the checklist - see below. Mandatory documents - Passport issued by my country ...

That is what I thought, the confusing part is this one - when they list all the documents I have already sent: " In addition to the missing mandatory required omission(s) noted above, when you submitted your application online via the Access UK website we requested that you submit certain documents ...

Hello, I have applied for the AN naturalisation through the online system on the 27th April, I have sent all the required documents straight after through the NDRS service. I have sent 4 photographs, 2 loose and 2 for the referees all with my name on the back. Yesterday I have received a letter from ...