Canterbury cathedral, the mother church of the Anglican communion and one of Britain's greatest architectural treasures, is suffering "serious damage" from pollution which threatens its long-term existence.
Such is the dramatic nature of the erosion to the structure and contents of the cathedral - which dates back to 597 and was founded by St Augustine - that its custodians are launching a global campaign to raise funds for repairs running into millions of pounds.
Cathedral managers said failure to complete the urgent work, which is understood to include the church's roof and its stained glass, would have "potentially disastrous consequences".
The building, which is one of only two cathedrals in Britain classified as a World Heritage Site - the other is Durham cathedral - is already the subject of a long-running fundraising appeal to maintain its stonework, glass and lead roof.
But there is concern that damage to the structure, including its walls of Caen limestone shipped from Normandy, is occurring at such an accelerated rate that an emergency worldwide appeal is needed. The church is one of Britain's top 10 tourist attractions with more than one million visitors a year, and the focal point of the Church of England.
In a statement, the cathedral's chief executive, Brigadier David Innes, said: "We are being forced to act as the cathedral is suffering serious damage through old age and modern pollution. Alas, time is not on our side, and if we don't start now, the rate of decay and damage will increase dramatically with potentially disastrous consequences."
Details of the worst examples of "new damage" will be made public when the appeal is formally launched on 3 October.
But the emergence of a serious threat to the future of a building of such architectural and historical importance highlights the increasing costs and dangers of maintaining ancient monuments in an era of dramatic climate change.
Stained glass in Canterbury cathedral, the scene of England's first murderous clash between church and monarch with the killing of Thomas Becket in 1170, is under threat from airborne pollutants that eat away at the panels.
The church holds some of the world's most dazzling medieval stained glass, including the 12th-century Oculus rose window. Its panels have been badly damaged by pollution.
Tiny pits are formed on the glass by a weathering "crust" which steadily thins and eventually perforates the glass. A team of conservators has protected many of the windows, but managers said "much still remains to be done".
One specialist said: "If stained glass windows are kept in their present state of preservation, their total ruin can be predicted within our generation."
There is also concern that fungus is attacking murals, and the Caen stone vaults are being eroded by moisture. Repairs to the lead roof are needed, and the one million visitors a year have worn away some internal stonework.
The need for a global cash appeal for the cathedral reflects the delicate balance of the Church of England's finances. The Church has sold property assets worth more than £1bn in the past decade as it battled to put its accounts on an even keel. It recorded a loss of £800m as a result of the 1980s property crash, and then had to cope with increased pension costs.
The church, which has assets valued at £4.3bn, has to fund the care and maintenance of 13,000 listed buildings, including nearly half of Britain's Grade I listed structures, such as York minster and Durham cathedral.
The National Trust, another major custodian of listed properties, warned earlier this year that climate change was affecting its historic properties. Since 2000 it has made more than 850 insurance claims totalling £7m for weather damage.
Saints and sinners
* The cathedral, founded in 597 by St Augustine, who was sent from Rome by Pope Gregory the Great to convert Anglo-Saxons, is the oldest institution in the country and a World Heritage Site.
* In 1170 four knights, acting on the words of Henry II, "who will rid me of this turbulent priest", murdered the then Archbishop Thomas à Becket at the altar because of his adherence to Rome.
* Within three years, Becket had been made a saint and Canterbury a place of pilgrimage, as chronicled by Geoffrey Chaucer.
* In 1538, Henry VIII ordered the destruction of Becket's shrine; a candle now marks the spot.
* In the English Civil War, it was damaged by Puritans.
* During the Second World War, roof-top patrols prevented incendiary bomb fires.
* The Archbishop of Canterbury, Dr Rowan Williams, is the 104th in direct succession to St Augustine.Reuse content