Just booked flights to Switzerland from the US transiting at LHR. We will not leave the airport, will just transit to a connecting flight. Best I can tell we do not need an ETA, but wanted to confirm with those who travel to the UK often (janis?).

Mel, an ETA is not needed for the UK as long as you are transiting AND do not need to go through immigration. I, along with three of my travel companions, just transited London Heathrow yesterday, flying from Washington, DC, to Heathrow on American and Heathrow to Kuala Lumpur on Malaysia. We landed in Terminal 3 and took the bus to Terminal 4, as we would have in the past. We were never asked for ETAs nor anyone else we saw transiting with us. If, for whatever reason, you missed a connection and need to stay overnight in London (at a hotel, not at the airport), you would need an ETA to enter.

One ticket or two? I assume all on the same booking so tripplanner is correct AFAIK

. . . "We were never asked for ETAs". Even when actually entering the UK and an ETA is required, one is not 'asked' to show their ETA. It is all electronic and Border Force will know if you have one or not . . .

Interesting...if you were to miss your connection, how would you get one on the fly?

Apply there and then and hope?

The original plan was for everyone, including airside transfers to need one, but that was later dropped.

They are pretty inexpensive and painless to apply for, and air travel as messed up as it can be sometimes with delays and cancellations -- IMO it would be prudent for anyone connecting through the UK to have one.

Okay, thanks I'll look into it.

You're correct janisj. It is my understanding that it functions similarly to Australian and New Zealander e-visas. Point is I nor my travel companions obtained ETAs and do not have it on file, so, answering Mel's question, we didn't need it on transit. As you and others have said, doesn't hurt to get it either. It's good for 2 years and isn't costly.