As there are 4 of us travelling together, can we all tap in with my bank card (and tap out at the end of course)?
My wish would be - passenger 1 taps in; passes the card back to passenger 2 who taps in; passes card to 3 to tap in; then passes to 4. And repeat at Heathrow.
No - see other advise. A very very dim view would be taken if you even tried this.
Ironic ...
My wife and I flew to Newark, New Jersey (yes, direct flights available from Heathrow) and used that PATH (Port Authority Trans-Hudson) into New York City. Struggling to work out our tickets at the machine (that's the same the world over!) a helpful member of staff told us to buy a multi-journey ticket, go through the gate one at a time and pass it back for the next person to come through. Standard practice there.
Is it any wonder that overseas visitor sometimes have trouble working out our systems, and we have trouble understanding how theirs work - in each case with penalty notices and warnings displayed to leave no doubt that you'll be in big trouble if you break the rules that you're not actually familiar with!