Hi,unofficially,complete a form on uk gov passport website,using a uk address,family or friends,they will post the completed forms to the address you use in uk,ask whoever to post it to you here,get the photos done here,then post it all back to uk to be posted on,or ask somebody going back to uk to take it post it on on their return,worked for us
can be done ldidnt have any probs when l had to renew my grand kids passports as l think l still have a contact number for them only took a couple of weeks from start to finish and that was over xmas time
If you are living here in Crete when your passport needs renewing, it seems to me that the easiest thing to do would be to make a short visit to the UK & use the premium one day service at the passport office. OK, it costs £129.50 ( plus flights etc!)as opposed to £77.50 for a normal passport renewal but it does mean that you don’t have to worry about documents getting lost in the post.
If you do what Mr Neumann suggests, then you have to send your old/current passport in when renewing. If you’re happy to live here in Crete without a valid passport that’s up to you, but I know I’m not!
Anyway, that’s what I propose to do when mine comes up for renewal. However, as that’s not until 2019 the regulations will all have changed by then!