Aye, so you don't care for the wee people doing magic in the early mornin' dew. :magic:
All mushrooms are fungus. What you see is the fruit, the plant lives underground (mycelium).
As the Fairy Ring grows larger and consumes the nutrients you get light green areas (which needs more nitrogen ) and Dark green where the Mycelium provided nutrients to the grass.
You can tell how old a ring is by measuring its annual growth rate and estimating the age.
Here in the US prairies it is said that some of our Fairy Rings are 600 years old.
So you wish to put an end to the Fairy Magic?
Use a good fungicide on the lawn. It is said that if you change the Ph of the soil, it will kill the Fairy Rings. However to be safe to the lawn just use Fungicide and
Bid the Wee Folks Fair Well
Mushrooms Demystified by David Arora