Funny smell on my neighbours allotment..

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 allotment 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.

The local council may be able to tell if it is methane.

...they think they have methane gas.  They took me in there and it really does smell a lot in there..

methane gas is odourless - that's why they used canaries in coal mines before technology caught up ... if the canary fell over, miners knew there was gas even if they couldn't smell it.

I know it sounds gross but a rotting animal body stinks to high heaven and can last for some time. We had a bird inside some cable ducting at work once

Check behind heavy stuff - it may have woken early and then been looking for a hidey hole as the temps dropped again.  Warmer weather makes the smell worse and few bugs are about yet to munch. 

I agree.  My guess would be a dead rat.   The man from the gas board told us that dead rats are responsible for quite a number of false call outs.  It bet it's under the shed.

Thanks for your replies.

As it smells a lot then it can't be methane.  We live in the midlands and there has never been coal mines around here.  The allotment site is approx 100 years old so i can't see it being a leaking gas pipe.  I'm not sure about the dead animal theory as they said they smelt it a bit last year....but what else could it possibly be?

I know it sounds gross but a rotting animal body stinks to high heaven and can last for some time. We had a bird inside some cable ducting at work once

Check behind heavy stuff - it may have woken early and then been looking for a hidey hole as the temps dropped again.  Warmer weather makes the smell worse and few bugs are about yet to munch. 

Good point forgot that bit!