If there is a gateway to hell, a portal from the underworld used by demons and witches to wreak their evil havoc on humanity, then it could be in a small east Midlands cave handy for both the M1 and A60.

Heritage experts have revealed what is thought to be the biggest concentration of apotropaic marks, or symbols to ward off evil or misfortune, ever found in the UK.

The markings, at Creswell Crags, a limestone gorge on the Nottinghamshire/Derbyshire border, include hundreds of letters, symbols and patterns carved, at a time when belief in witchcraft was widespread. The scale and variety of the marks made on the limestone walls and ceiling of a cave which has at its centre a deep, dark, hole, is unprecedented.

Believed to protect against witches and curses, the marks were discovered by chance at the site, which is also home to the only ice age art ever discovered in the UK.

Paul Baker, the director of Creswell Heritage Trust, said the marks had been in plain sight. They had known they were there. “But we told people it was Victorian graffiti,” he said. “We had no idea. Can you imagine how stupid we felt?”

The trust was alerted to the marks last year by Hayley Clark and Ed Waters. The two keen-eyed cavers thought there were perhaps two or three markings; it soon became clear there were dozens and then on further investigation up to a thousand. And counting. “They are everywhere,” said Baker. “How scared were they?”

Facebook Twitter Pinterest Members of the Subterranea Britannica group check out the witches’ marks at Creswell Crags. Photograph: Historic England/PA

There is no public access to the cave but the trust is considering a multi-media presentation for visitors.

Up close the walls are a remarkable frenzy of marks. Everywhere you point a torch there are overlapping Vs, a reference to Mary, virgin of virgins. There are also PMs, as in Pace Maria, and crossed Is, referring to Jesus on a cross, and odd-shaped As.

Alison Fearn, a Leicester university expert on protective marks, recalled first shuffling on her backside in to the cave and realising what she was looking at. “I think I said a very naughty word.”

The letters and symbols were Christian but should not be looked at in that context, she said. From the 16th century to the early 19th century, when people made witches marks, there may have been a lack of association with religion, such as today when people might cross fingers or say “oh god”. She said: “It just becomes a protective symbol. It was a mark you always made to protect yourself.”

What the marks were keeping out, or in, can only be speculated on. “It could be fairies, witches, whatever you were fearful of, it was going to be down there.”

Creswell Grags Creswell Crags

The cave markings fit in with local history since the post-mediaeval village of Creswell used to be much closer to the caves. The dukes of Portland had relocated the village 20 minutes walk away during a spot of 19th century landscaping for themselves.

John Charlesworth, the caves’ heritage interpreter, said natural landscapes were once regarded as scary places. “These are places where supernatural forces in an untamed non-human environment could be at work. Local people are in the jaws of this monstrous landscape.”

Ritualistic protection marks are most commonly found in houses and churches, in doors and windows, to ward off evil spirits. They have been found in caves but never on this scale.

Facebook Twitter Pinterest Macbeth’s witches from the Illustrated Library Shakespeare published in 1890. Illustration: Universal History Archive/UIG via Getty Images

Creswell Crags hit the headlines in 2003 when ice age cave art, including figures of birds, deer, bison and horses, were discovered.

The announcement of the latest find was made by Creswell Crags and Historic England. Baker acknowledged that the witches’ marks might bring a new type of visitor.

Ronald Hutton, a professor and leading authority on folklore, said the find was hugely important and exciting. “It looks like the largest assemblage of protective marks ever found in British caves, and possibly anywhere in Britain.”