A preserved brain from Iron Age Yorkshire has puzzled archaeologists over how the soft tissue has survived almost intact.

The skull was studied by Rachel Cubbitt from the York Archaeological Trust. "I peered through the hole at the base of the skull to investigate. To my surprise saw a quantity of bright yellow spongy material. It was unlike anything I had seen before," Cubitt told Culture 24.

The spongy brain matter was discovered in a skull from an ancient pit in York, and by looking at the teeth and the shape of the skull, scientists say it is likely this person was a man between 26 and 45 years old.

Archaeologists who have examined it say the brain has a "resilient, tofu-like texture", while the jaw and two vertebrae were still attached to the skull.

Known as the Heslington Brain, the individual is believed to have been hanged before being decapitated with a knife.

"An examination of the vertebrae in the neck tells us that he was first hit hard on the neck, and then the neck was severed with a small sharp knife," said a spokesperson for the York Archaeological Trust.

The skull appears to have been buried immediately, although the rest of the body was missing. Although it is not known why he was killed, one theory suggests this could be a human sacrifice or ritual murder.

Scientists are still trying to discover why the Heslington Brain is so well preserved and in such good condition, making it the oldest preserved human brain in Britain.

Its excellent condition may have been helped by the immediate severing of the skull from the body.

The head was cut off from the alimentary tract and drained of blood, so the intestinal bacteria could not contaminate it.

"It was just amazing to think that a brain of someone who had died so many thousands of years ago could persist just in wet ground," Sonia O'Connor from the University of Bradford, told Live Science.

"It's particularly surprising, because if you talk to pathologists who deal with fresh dead bodies they say the first organ to really deteriorate and to basically go to liquid is the brain because of its high fat content."