What you need before starting the ETA application
Use the passport you will carry on the journey. Prepare the passport number and enter every name in the same order and spelling shown on its biographical page. The application is linked electronically to that passport, so submitting details from an expired, cancelled or different document can cause problems when the carrier checks your permission.
You will also need a clear image of the passport photo page, a suitable recent photograph and an email address you can access before and during travel. Keep the face fully visible and follow the image instructions shown in the application. Travel information can help you complete the form accurately, although you should not invent flight details that are not yet available. Every eligible traveller needs a separate UK ETA application, including babies and children; an adult may complete it for them using each child’s own passport.

