Hey!
In a similar situation. Not sure if my British passport will come in time so am in the process of getting my EU passport back and British Citizenship (supporting documents)
You can ring the advice line 0300 222 0000 (I believe?) The first number you press on the call line will be 8, then 3. You will be put through to an advisor. Explain you need your documents back and they can arrange for a call back from the ‘Customer Service Management Team’ within 48 hours. I’ve been told you just need to prove that you need them urgently for travel (not sure how as I am still waiting for call back!)
It will pause your British passport application, and they ask to send back your documents within 6 weeks (otherwise they drop your passport application I think?)
I hope this helps! I can update when I’ve got a call back and my own documents if that helps?
🙂