Change to Fast track in person appointment

Having read many posts here I am not convinced Ill get my passport back by 25th April - brexit changes meant my passport issued on 24th April was not valid in EU even though expires in November! I now wish id gone fast-track and could get to London for an appointment quite easily and would "save" money by going this route. How does one do this if current passport is at the Liverpool office? I have heard nothing on app since last week when documents received, but spoke to someone on Friday who said its been sent to examiners re:photo. I can wait to see a bit but in a while I'd like to go the in person route and just head to london to get my passport - how do you do that if its going the online route too and they have your passport? I hear it takes weeks to get passport back from Liverpool.