Allotments 4 All

Just been to my allotment and for the last 3 or 4 weeks, I have sometimes smelt something which I put down to being a paraffin heater in my neighbours greenhouse.  My neighbour spoke to me today saying that they have a problem in their greenhouse...they think they have methane gas.  They took me in there and it really does smell a lot in there.  I asked them if they used a paraffin heater or have any old paraffin lying around which may have tipped over but they say they have never used one.  They are going to speak to the committee to get advice but I wondered if anybody on here could shed any light on it. 

Does anybody know what it could possibly be?

Thank you for your replies.

Armillatox as a cleaner smells like that as it fades...

I'll ask them.  Thanks

Not near old mine working?

Some people soak their peas in paraffin to deter mice.