The chick, named Celia, hatched three weeks after Miles Orford, of Great Ashfield, placed six free-range Cotswold Legbar eggs in an incubator.

His mother, Sarah Orford, said: "We've tried the same experiment with quail and duck eggs.

"None of the quail eggs hatched. We're still waiting to see what happens with the duck eggs."

Mrs Orford bought the eggs from her local Waitrose store.

"We read about someone who had done it with duck eggs and thought we'd experiment," she said.

"I have to say I was somewhat surprised. It's very interesting."

A fresh egg

How the egg came to be fertilised is not known.

Free-range egg farmer, Phillip Greenacre, told BBC news: "Well it could have happened by a rogue bird from a neighbouring farm or more likely a bird from within the farm that didn't get sexed properly."

Francine Raymond, of the Henkeepers' Association, said the average person wouldn't be able to tell the difference between a fertilised and non-fertilised egg.

She told BBC news: "After about three weeks you wouldn't be able to hatch it - it was obviously a fresh egg."