Heathrow Terminal 1 Transfer
 

We will be arriving Terminal 1 on United from SFO and transferring to Swiss Air also in Terminal 1. From the Heathrow website it looks like we will need to go thru security again, even though we never have to leave terminal 1. ..Is this correct?

Yes.

Several years ago I took a mileage trip to make AA Platinum again. RT SFO-LHR and back after a 3-4 hour layover.

I had to go through a customs variation. I didn't actually leave the boarding area, but I had to go through a security check to get something stamped on my passport or boarding pass to be able to gat back on the plane.

The things one does to keep elite FF status.

You will have to go through ordinary security - hand-carry x-ray, metal detector, passport and boarding pass check, etc. - should be easy and hopefully quick. Follow the signs to "flight connections." You won't have to leave T1.

PS There is no SwissAir (bankrupt years ago) - it's now Swiss International Airlines, a different outfit.