Hi
I haven't made any kind of passport there but I have used their notarial services and affirmation services. But I do know for any kind of documentation required there is now quite a stringent procedure that must be adhered to, Below is a cut and paste from their site (forgive me, if you have read this):
You must make an appointment for each service that requires your personal attendance. Before booking, you will need to complete a service request form and email it together with your documents to: notarialservices.hanoi@fco.gov.uk.
The embassy will confirm if the service can be provided and where it can be carried out. The embassy will also provide you with a link to book your appointment online and a reference number. You must quote this reference number in the ‘comment’ box under the ‘additional information’ part when booking your appointment.
A couple of years ago you could just walk in and chat with someone but that has changed completely. You do need to go through the procedure to obtain any kind of entrance into the building - as far as I am aware and from personal experience. I would imagine obtaining any kind of passport etc would certainly require personal attendance. It is a strange set up. When I needed earlier this year an affirmation from the Consular that I had no wife in the UK I had to go through exactly as above. It involved sending an email to ask if the service I required was available, then an affirmative response came with the necessary forms attached which I had to print off and physically sign and then scan and send back via email with the fee that was required and then I had access to the part of the website that allowed you to make an appointment at a time of your choosing. A strange set up in this modern world; to download, print off, sign, scan, and email back. Rather long-winded but there was no way round it.
Perhaps someone knows differently, then forgive me, but I would imagine - if a passport replacement extension/extra pages etc is available at the Consular - it will be a long-winded procedure but at a lot of time can be saved by just starting at the point that they say to start and as mentioned earlier. I can't imagine any kind of passport procedure would even begin to initiate if the holder is not there in person. I could be wrong of course.
But is that service available at the Consular in HCMC or the Embassy in Hanoi?
Passport renewal is not actually not on their list of services required. Emergency travel documents are, but there is no mention of passport renewal or extra pages etc. All UK passports in Asia are now supposedly processed via Hong Kong. It may be a case of renewing online via the Gov UK website, sending your passport back to the UK, and then DHL it back out here - from a UK address - they won't send it abroad. Perhaps a lot less hassle and a few weeks lost and a cost of about £50 (for the postal service, not the passport) to send it back in 3-5 days with guaranteed delivery.
Good luck with all anyway. I hope it all works out
8-)