Renewing passport, no UK address any more

[Shouldbedoing]

A friend is travelling to UK soon to renew her British passport in person. She lives in Turkey. Trying to apply for the passport online they need her address and it must be a UK and secure address for posting back the passport. Now she's unsure what address to put on her In-Person application. She lives exclusively in Turkey. Can anyone advise, please?

All went well, in person at the Passport Office, left with her physical Passport after a 4 hour wait

That’s a relief, OP, glad it went well for your friend.

I did the same thing a few years ago, booked an overnight stay in London in case it wasn’t ready the same day-but it was by late afternoon.