This is my recent experience : my wife and I both needed new passports as hers expired six months ago and mine expired around ten days before we applied In mid February this year.
Looking on line at the procedures and options to renew a passport I decided that going to a Post Office and letting them do the complete application online seemed a good idea. So we went in to the main post office only to find that they offer this by appointment only so we duly booked an appointment for the following week.
We attended on the day at the allotted time and the process was smooth and hassle free. They take your photo with the appropriate background and then with an iPad device ask you questions ( see below ) and input the answers. At the end we were asked to review the information on the screen and click to confirm if all was correct Before submission.
The fee was £103.50 for each of us and that included ( if I remember correctly ) £5.00 to have it returned to you by tracked delivery and also the separate return of your old passport. The Post Office clerk said to allow up to six weeks but ours landed in precisely 14 days and the old passports arrived back with us about two weeks after that.
One may consider the fee a bit steep but I had to have a photo taken to renew my driving licence last year and that cost me £8.99 so allowing for that and then the costs of postage I reckon that the fee that we both paid was reasonable and because the entire process was so easy.
#### TIP ###. Before we went in to the Post Office I printed on a piece of plain paper all of the info I thought would be required so on this piece of paper I put
Full Name.
Date of birth.
Full address including the correct postcode.
Place / location of birth.
Any previous names, i.e. a maiden name.
Contact telephone number.
email address, an absolute requirement.
By providing all of the above info printed clearly it removed the necessity for the counter clerk to keep asking questions and also avoided the “how do you spell that ?”
We received email updates from the Passport Office, the first one to confirm that the application had been received.
Then one to say it had been processed, being sent which include tracking info but being delivered by a courier.
Then the couriers kept us updated with delivery date and timing.
As for the return of the old passports, they came via Royal Mail which again was tracked and we had emails to keep us abreast of delivery.
I am aware that my post does not fully answer the original question posed by Chris S but I thought my recent experience may prove useful to some. If you do decide to use the Post Office for this service bear in mind that not every P.O. offers the service but a search online will bring up the main P.O.s that do.