Thank You for replying.
It is not their fault for missing the connection. Even Swiss did not make such a ridiculous comment except one arrogant customer service agent from South Africa.
It was one ticket, they were in the UK as You have assumed, they transited thru UK as well.
They followed instructions to go to Transfer Desk given during the flight, but noone told them that it is in different terminal (E) and there is a passport control. Other passengers apparently had Shengen visas and were able to go thru, while my friends - were stopped. There were NO SWISS agents at the terminal D to assist them and passport control agents could care less. Everyone quickly left the Terminal D and airport was "closed".
They have spent 15 hours at the airport. You are the only one who thinks otherwise.
Thank You for your input.