Horrible histories: Why has a Lancashire school's set of grisly religious relics been hidden for years?

It's one of the most gruesome collections you'll ever cast your eye over. Nick Clark discovers its bloody secrets.

It is the biggest collection of relics in Britain, but few will have heard of it. Now the curator of the historic Catholic school that houses the archives of eyes, skin, skulls and even a part of the supposed Crown of Thorns hopes the funds can be raised to put it on full public display for the first time. Items from Stonyhurst College's collection are increasingly loaned for exhibitions, with one of the grisly jewels in the crown currently on display at the British Museum's "Shakespeare: Staging the World" exhibition.

The show, which opened this month, brings together a series of objects from Tudor England to help conjure up the turbulent times for a 21st-century audience. Undoubtedly one of the star attractions will be the eyeball held by Stonyhurst from a Catholic martyr who was executed in 1606.

The eye's owner, Edward Oldcorne, was unlucky to have been caught. He had long survived as a Catholic priest at a time when it was treason, yet was picked up when other priests, fleeing arrest in the aftermath of the Gunpowder Plot, sought refuge in his house. He was publicly hanged, drawn and quartered. The eye was fished out of the pot used to boil his body, the process to prepare it for public display, and put in a silver reliquary to preserve it.

The religious relic speaks to the persecution of the Catholics in Britain in the 17th century and is just one of the items held in an extraordinary collection at the independent Jesuit school. Jan Graffius, the curator of the school's collections, says: "Some things have a powerful ability to speak. We all know how sensitive the eye is and how precious our eyesight is. To see a human eyeball in that state, you can't fail but be moved. I've never shown it to someone and not got a reaction, whether shocked, appalled or horrified."

Stonyhurst traces its roots back to 1593, when the English Jesuit College was founded in Saint-Omer to offer a Catholic education to English boys abroad. The persecution of the Catholics made it impossible in Britain.

As well as offering Catholic pupils a sanctuary, it preserved manuscripts, vestments, prayer books and relics rescued during the English Reformation. Many relics were handed down by Jesuit families and often given to the school for safe keeping. "We were founded out of persecution and based abroad; these objects were shipped over to keep them safe," Graffius says. Examples include the shoulder blade of one of four Catholic priests executed in Durham in 1590. The bones bear the clear mark of knife slashes where the victim was quartered and some skin still remains attached.

Relics are believed to have a power and there are many instances of miraculous cures with those that have been laid on the sick, she says. "Although many have miraculous traditions attached to them, they are simply there to help the faithful deepen their faithful contact with someone who was a servant of God."

Believers have looked to relics from the earliest time of worship. "The early church was persecuted and the martyrs were put to death in particularly gruesome ways," Graffius says. "People want to meet at those places to commemorate them. That became a tradition. The early Christian churches were built over the graves of these martyrs and there are still relics inserted into altars."

The practice was recorded in the UK by the Venerable Bede writing in 731 in reference to St Chad of Lichfield – a part of whose skull is at Stonyhurst, incidentally – where people would mix dust from his coffin with water to cure illness. "The ultimate test is not whether these things are real – they don't have magical powers – it's if you believe they are important to your prayer life," Graffius explains. Different relics were used for different ailments and conditions "but the Holy Cross pretty much did everything".

Stonyhurst has a piece, hardly bigger than a splinter, of the supposed True Cross upon which Jesus Christ was crucified. Yet its most prized possession is a thorn believed to have been part of the Crown of Thorns. The relic, which has a pearl necklace that was owned by Mary Queen of Scots wrapped around it, can be definitively tracked to the eighth century, but has not been removed from its centuries-old reliquary for further dating tests. The thorns were supposedly found by St Helena and taken, with parts of the cross, to Constantinople.

The capital of the Byzantine Empire was looted by the Crusaders in 1204 during the Fourth Crusade and many of what were held to be the relics from the crucifixion ended up in Venice before being bought by the French King Louis IX. The French kings would break off thorns from the crown and give them to those who married into the family. A pair was given to Mary Queen of Scots, who wore it in a locket.

The collection has a series of objects from the Stuarts, as the school was sympathetic to their cause. It includes the prayer book Mary took to the executioner's block. She is believed to have swapped it out at the last minute for a less valuable volume, as she knew whatever she was holding would be burnt. The book has been with the Jesuits since the 1640s and went back to Scotland last year for the first time as part of an exhibition. Graffius was not prepared for the anger from sections of the Scottish media, which demanded the volume be returned to Scotland.

The last English Roman Catholic monarch was James II, who died 13 years after being deposed during the Glorious Revolution. In Stonyhurst's collection is a reliquary that has some of the monarch's flesh, hair and blood. "We have a lot of body parts," Graffius admits.

There are three canonised saints among the school's alumni and a further 10 beatified martyrs. "I'm very strict on how we treat relics particularly when we're showing them to children," Graffius says. "We don't put them on display as some sort of freak show."

Continental Europeans are more used to the idea of relics and occasionally whole bodies of saints are on display in places of worship. "In Britain during the Reformation this was very much stamped out," Graffius says. "The Anglican tradition doesn't have the same dependence on relics, so British people became unfamiliar with them. It's not really part of the British faith."

Beyond the religious collection are a series of Tudor treasures including prayer books and manuscripts from those who helped shape Britain in the 16th century. One book bears the signature of Elizabeth Plantagenet, sister of the Princes in the Tower and mother of Henry VIII.

Watching over the collection is the skull of John Morton, who tutored the Princes and Elizabeth before his arrest by Richard III. "He's very special," Graffius says.

Upon his release, Henry VII appointed Morton to the post of Lord Chancellor and he came up with "Morton's Fork" system of taxes that was familiar into the 20th century. He is also believed to have written the account of Richard III, later rewritten by Sir Thomas More, who had been in his household, which formed the basis of Shakespeare's play. Morton's skull ended up in Stonyhurst after Oliver Cromwell's troops smashed open his tomb in Canterbury Cathedral and pulled out his bones. A local Catholic rescued the head.

It is unclear quite how many relics are in Stonyhurst's collection as it is still being catalogued and some are yet to be authenticated. Authentication is done by a bishop, who listens to the evidence and gives approval for newly discovered items or even when an item is taken out of its housing.

The collection of the college, which moved to England in 1794, is believed to be the oldest and most comprehensive of its time in Britain. It finishes in the suprisingly recent past, with a piece of bloodied vestment from a bishop murdered in El Salvador in 1980, Oscar Romero.

The Christian Heritage Centre is seeking funding to make the collection publicly accessible for the first time, estimated to cost more than £10.4m. Graffius is leading the drive to make the collection more visible and objects have been loaned to institutions in Britain and abroad. But transporting body parts has not been smooth sailing. She was stopped a US airport when customs officials discovered a human leg.

"The leg of St Thomas of Hereford caused consternation. You're travelling with human remains and people get taken aback," Graffius says.

Eventually she was allowed through when the chief of customs, who happened to be a Catholic, sorted the situation out. "He immediately understood. But it brought it home… to me this is perfectly normal; it's not regarded as perfectly normal in the rest of the world."