THEY survived the Reformation, the Civil War and German bombing raids, and have become revered as one of the finest collections of medieval stained glass in the world.

But now, an historic church in the heart of York faces having to launch a huge fundraising drive amid fears that its priceless windows could otherwise be irreparably damaged.

A survey of the glass at All Saints’ in North Street, some of which dates back to the mid-1300s, has indicated substantial paint loss, and experts say that unless action is taken imminently, the windows will continue to deteriorate.

The combined effects of condensation and natural erosion mean some intricate details, such as on figures’ faces, have already faded, including on The Pricke of Conscience Window, one of the church’s most treasured pieces.

York Glaziers’ Trust is now working on a detailed report, which is expected to recommend work costing several hundred thousand pounds over the coming years. The precise cost is not yet known, but the church envisages launching a nationwide fundraising appeal later this year.

Churchwarden Robert Richards said: “We always say these are not just pretty pictures – they are aids to spiritual devotion. We are waiting for the details, but we think it will certainly be a national appeal.”

Sarah Brown, director of the Trust, said it was an “immensely important” project.

Sarah said it was rare for a church to have so many surviving medieval pieces of stained glass.

She said the variety of subjects found at All Saints’ is uncommon, as is the amount of detail known about their donors or sponsors. “There is an opportunity now to use preventative conservation techniques to safeguard these windows for the future.

“It is possible to intervene, and the windows can be preserved,” she said.

Experts from the Trust have been examining the windows with a microscopic camera and comparing the windows with older photographs to assess the deterioration. Nick Teed, senior conservator at the Glaziers’ Trust, said protective layers of clear glass could help slow the erosion, but further work may also be needed, including to counter the effects of adhesives used to repair old cracks.

All Saints’ North Street became famous in the 15th century for a series of prohetic visions experienced by Emma Raughton, an anchoress, or hermit, living in a locked room at the rear of the church.

The Virgin Mary reportedly visited her seven times, correctly prophesying a series of incidents including the death of Henry V and the coronation of Henry VI in France, and sparking a wave of pilgrimages to the church.

Church’s windows on the world

The Pricke of Conscience Window dates from 1410 and is based on a medieval poem of the same name.

It foretells the final 15 days of the world, in words and pictures in a series of panels. It is regarded as unique in Europe and is also unusual for being written in English rather than Latin.

The Corporal Acts of Mercy Window was bought by, or in memory of, Nicholas Blackburn, a merchant and Lord Mayor of York. It depicts six of the seven acts of mercy from Matthew’s Gospel, including feeding the hungry, clothing the naked and visiting the sick.

The Blackburn Window behind the altar was also given by the Blackburn family, in the 1420s. The foot of the window shows Nicholas Blackburn senior and his son, Nicholas junior, kneeling with their wives, below depictions of St Anne, St Christopher and St John the Baptist.