Anyway, I'd finished watching Cliffhanger on the TV and went to check my email before going to bed. And shortly thereafter felt slighty nauseous and smelled gas. So I went round the house and checked everything. I hadn't left the oven on or anything. But the smell was still there. And outside. So I rang Transco and we went through the usual palaver. An engineer duly arrived at about 02:30 and found nothing. But the smell had gone. He left a bit after 03:00
We reckoned it was fuel - or something else - dumped by an aircraft.
Still, going to bed at that hour is not fun. I must be getting old...