Links:

Apple recovery contact:

    - https://support.apple.com/en-gb/102641
    - https://support.apple.com/en-gb/102608
    - https://support.apple.com/en-gb/118574

iPhone Stolen Device Protection:

    - https://support.apple.com/en-gb/120340

giffgaff lost phone:

    - https://help.giffgaff.com/en/articles/233996-i-lost-my-phone-what-should-i-do

https://www.moneysavingexpert.com/mobiles/steps-to-take-befo...

Check whether any two factor authentication apps you use support backup, and plan how you will regain access to accounts that require them.