http://ukinhongkong.fco.gov.uk/en/help-for-british-nationals/passports/what-passport/renewing-passport/steps-to-renew wrote:Countersignature of the form and photographs is not necessary for those people over 16 renewing a passport, unless your appearance has changed significantly since your previous passport was issued.
Countersignatures on the back of your photographs are not necessary and the countersignature box on the application form does not need to be completed if your appearance has not changed significantly since your previous passport was issued.
However, the notes for the smart passport form (linked from the same page) don't mention that a countersignatory isn't necessary in this case. So, just to be sure, has anyone successfully renewed a UK passport in the last year (after the switch to processing in London), without getting the form and photos countersigned?
I did search but only found old threads:
Passport renewal in Taiwan (2010)
UK passport processing - FYI (2010)
Any qualified British teachers living in Taipei (2005)