text: how do you find out your old passport numbers (british passport)? i have to give a list of all the passports numbers i've ever had for an immigration document.  i've had at least 5 over the years (i travel a lot and therefore go through them pretty quickly), but have no idea what their numbers are except the most recent which i currently have.    nb these are british passports. i would phone a issuing office, they would if anyone keep a record of your old passport numbers. i would guess for secity reasons there would be a bunch of forms to fill in as well.