ETA requirements

You should have received an email indicating that your ETA was approved. Did you get that? In early 2025, mine was sent from the UK Visas and Immigration Home Office.

You don’t need anything other than your passport for UK passport control. The ETA is associated with your passport number.

Some people have reported being asked by the airline to show their email confirming the ETA. You are not supposed to have to do this.

One more thing …
The UK now has a toolwhere you can check validity:
https://www.gov.uk/check-eta

As noted above, your ETA is electronically linked to your passport. Passport control is egates, so there's no-one to show it to anyway.

There is a very small chance your airline may ask when you check in (they are supposed to be able to check automatically), so to be on the safe side you can use the web site above as evidence.

As others have said, your ETA is electronically linked to your passport. We received ours in January for our upcoming trip to Northern Ireland. On the day we applied, we each received an email from the UK Visas and Immigration Home Office confirming we have the ETA. The email does state that we "do not need to print or show this confirmation email." However, I have printed both of them, and we will bring the emails with us. My philosophy is to be better safe than sorry. You just never know when someone might ask for it.

This might not be relevant, but when we flew from Sydney to Christchurch, NZ, the airline asked to see a hard copy of our NZeTA, even though it was linked to our passport. I didn't know they would ask to see it; however, I printed them out and brought them with us, just in case. I am probably paranoid about this sort of stuff, but you never know.