She says Steiner’s son and two Sizemore students were on the bus with him when it was hit head-on outside Kampala, the Ugandan capital.

Steiner, 25, is a graduate of the Culinary Institute of America with a passion for drinks and chatting up guests.

But patents covering such substances have been a sticking point in past discussions, says Achim Steiner, until recently the head of the UN Environment Programme.