No agents, no professional pictures, no counter signatories and no UK visit required.
This is recent information as of two months ago.
I applied online with the HMPO website while in Thailand.
Uploaded my own telephone pics which were checked and accepted by the website.
Paid with my UK credit card.
Sent my old passport to HMPO from Thailand with priority EMS at post office.
Used my sister's UK address for delivery.
When my sister received my new passport, she posted to Thailand with Royal Mail tracked/signature/airmail service.
From online application to receipt of new passport in Thailand took six weeks.