Its virtually impossible for an animal to get under there and I am more inclined to think that its a sewage type stink than a dead animal.
There isn't a vent pipe nor is there a stack vent on the outside.
But as I say, this is a recent problem and not something that's being going for long at...
The story is as follows:
identified a water joint leak under the toilet/bathroom floor which must have been running for a year.
Had the floor pulled up and pipes repaired, ground dried out etc.
Now had the bathroom and toilet refitted but since had a drain blockage in a few doors down...