Cook Maria Mills has probably cracked open thousands of eggs in her 11-year career, so she was hardly eggspecting this one to be any different.

But to her surprise, it turned out to be rather eggstraordinary - another perfectly formed but smaller egg nestled inside the shell.

Maria works for Arun District Council as a housekeeper and was making egg mayonnaise sandwiches when she made the unusual discovery.

Maria, of Littlehampton, works at the Civic Centre in Littlehampton. Arun District Council has its full council and cabinet meetings there and Maria provides all the catering and refreshments for civic events.

She had boiled a pan of eggs to make the sandwiches and peeled off the shell of the outer egg.

When she cut into the egg to slice it for sandwiches, she hit the hard shell of the second egg inside.

The small egg was sitting where the yolk of the larger egg should be.

Maria said: "I was opening hard-boiled eggs to make sandwiches when I discovered the mini egg inside.

"I can honestly say I've never come across anything like it in my many years of catering experience."

There have been reports in the UK of similarly strange eggs but Linda Turvey, who runs the chicken and turkey sanctuary Hen Heaven in Henfield and handles millions of eggs a year, has never seen one.

She believed it was a result of a hen's internal production line going haywire.

Linda explained that the shell and egg colour are the final parts of the process.

She said the yolk was created, then the white, followed by the shell and colour.

The mini-egg may have become stuck while the second egg was making its way along the production line.

Linda said: "I don't know why it happens or how but its obviously something which happens along the hen's production line.

"I had a turkey's egg which had another membrane and albumen over the shell.

"It just means something has gone wrong along the way."

All eggs, whether free range like Linda's or mass produced, are "candled".

This is where a light is shone through the shell to help spot anything inside which may make them inedible.

Linda candles dozens of her eggs by hand but has never seen anything like this.

She added: "Perhaps it was sat on the light box and the person who was supposed to be looking at it blinked and it got through."