Passport application - how was your experience?

Hi, sorry if this is not the right place to ask 😅

I’m getting my naturalisation certificate next Monday (17th) and I will need my passport, the current one I own, a month from that (18th of December).

I read that most people had to send off their current passports to get a British one, but others were successful in uploading pictures of every page(?) has anyone had this experience?

I also read that they usually send back your supporting documents separately from the new passport, but I can’t find information on how long that usually takes.

Are they reliable with sending supporting documents back quickly?

Thank you!