Shortly after I moved to Cambridgeshire I had a job for a farmer, clearing a load of trees around a derelict house. To keep costs down he asked me to burn it all on site, which I did. It was a pretty big fire and a few days later he rang up asking if I had a digger.....
Turned out the fire had set alight to the peat layer under the ground, as a lot of this area is ancient peat bog. Fortunately we had two days of torrential rain and it went out, as I later found out underground peat fires can burn for years, it just smoulders away underground and pops up every now and again. They can cost thousands to put out, as you literally have to dig them out.
Narrow escape I feel!