Tucked away in a Chilterns valley five miles from Henley on Thames, Stonor possesses both a grandeur and a seclusion well-suited to the needs of the family who have lived there for over 800 years.

The magnificence of the house, with its park, beechwoods and fields, testifies to the status of the Stonor family, notable since the Middle Ages.

That air of seclusion, though, bears witness to something else a compelling need for privacy. The Stonors were staunch adherents to the Catholic faith through dark centuries of persecution.

Today, besides viewing the family portraits, tapestries, bronzes and ceramics, visitors can also see the secret room occupied by St Edmund Campion, Jesuit and martyr.

During the 1580s, he and his companions ran a clandestine press at Stonor, and there printed a celebrated pamphlet arguing against the Established Church of the time.

Built against a rising slope, the house itself is climbinge on an hille' in the words of the antiquary John Leland who visited Stonor under Henry VIII. At that time the mansion consisted of two courts buyldyd with tymber, brike and flinte'.

Today the E-shaped Tudor manor has soldierly ranks of Georgian windows set into the red brick faade, and both the house and its chapel incorporate fanciful features in the 18th-century Strawberry Hill Gothic Style.

But the core of Stonor is much older. Within the architectural jigsaw are remnants of a mediaeval house built of flint, chalk and clunch from the late 12th century.

Mass has been celebrated either in the chapel or house at Stonor continuously since the time when Sir John de Stonore (1280-1354) was Privy Councillor and Chief Baron of the Exchequer, and his son fought for England at Crecy.

At that time, the family fortunes were flourishing. Through the wool trade, marriage and high salaried office the Stonors acquired properties as far off as Cornwall and East Anglia. Heads of the house counted themselves friends of royalty and their fragrant, thyme-flavoured Stonor venison was favourite fare on the banqueting tables at Court.

One symbol of wealth was the chapel's brick tower, built in 1416-17 by Les Flemyngges' a community of Flemish brickmakers who had settled in the Chilterns from 200,000 bricks made at nearby Nettlebed. This was among the first uses of brick in southern England since Roman times. It must have looked futuristic in its day.

The Protestant reformation put a stop to the boom times. After Henry VIII's breach with Rome, the Stonors stubbornly continued to adhere to Catholicism and refused to take the Oath of Supremacy which made the reigning monarch head of the English church. They and Catholic families like them were known as recusants'.

Besides having to pay crushing fines for refusing to worship at the Established Church they became social pariahs for over two centuries, isolated from the Protestant gentry, barred from public office and the magistrates' bench, prohibited from sending their sons to public school or university.

Particular calamity fell on Stonor following Edmund Campion's clandestine printing activities there. The Jesuit was eventually caught, tortured and executed. In the furore, Stonor itself was raided, and the printing press and much massing stuff' were seized. Among several people arrested were John Stonor and his mother Dame Cecily who were both sent to prison.

Further imprisonments and continuous heavy fines for recusancy, meant that by 1650, the family had sold off all its estates except Stonor itself. For obvious reasons, little work was done on the house during the years of persecution. By the middle of the 18th century, however, a greater toleration led to a revival of fortunes. The house acquired its Georgian front and the Gothick features were introduced.

With the Catholic Emancipation Act of 1827 the Stonors were again allowed to hold public office. Thomas Stonor became MP for Oxford and was granted the ancient Barony of Camoys. Known as Old Tom', he threw himself into public life with relish. Besides becoming High Sheriff of Oxfordshire he was Lord-in-Waiting to Queen Victoria under six administrations, serving for a record 32 years. Old Tom was also a founder of the Henley Royal regatta and an early member of the MCC.

Thomas Stonor created the dining room at Stonor, memorable for its wallpaper of 1816 showing the great buildings of Paris all lined up artificially, side by side, along the banks of the river Seine. Other notable rooms include The Library containing an important collection of Catholic books, many illegally printed or smuggled in from abroad. The Study has fine Italian drawings as well as two paintings of pairs of heads from The Circle of Annibale Carracci. The most astonishing room though is Francis Stonor's Bedroom, with its outrageously showy shell-shaped bed and shell chairs. They were bought in Paris by one of the most flamboyant sons of the house.

This year, new attractions include an exhibition of American Ancestry. The present owner, Lord Camoys, is descended through his paternal grandmother from the Brown and Sherman families who left England in the 1630's to settle in New England, subsequently rising to American eminence both in public affairs and artistic circles. The exhibition includes portraits, photographs, prints, porcelain, glass, silver and sculptures of two families who were among the earliest American collectors to visit Europe regularly in the 19th Century.

Outside, you may see red kites hovering over the Italianate walled garden that sits behind the house on the rising slope of the hillside. Near the chapel is a prehistoric stone circle, reconstructed in 1980, but evidently a very ancient feature of the site suggesting that the remote valley was already a place of worship in pagan times. Stonor means stone hill' and some of the sarsen and pudding stones' were in fact incorporated by the mediaeval builders in the wall of their chapel, as if to stress a continuity of faith between the Christian Church and an older religion still.

The secret printing press Oxford in the 16th century was an intellectual centre for Catholics reacting against the Reformation, and there were many families adhering to the old religion in the countryside around. When the Elizabeth I came to the throne, however, scores of Roman Catholics fled the university city to seek refuge on the Continent, some settling at the seminary of Douai in the Netherlands, a centre of Catholic teaching. After training there they returned to England as committed missionaries, strong in faith and ready to die to advance their creed.

One of these was Edmund Campion, who had been a brilliant young scholar at St John's in Oxford. In June 1580, following training at Douai, he landed at Dover disguised as a jewel merchant, and began moving from one Catholic house to another, offering Mass, encouraging fainthearts and reconciling Catholics who had lapsed from the old faith.

In the great house at Stonor he was made especially welcome, and emboldened to set up an illicit printing press for disseminating his creed. With Robert Persons, Stephen Brinkley and others he converted a space high up in the house, behind the chimney, to conceal the press. It was from Stonor that, in great secrecy, he issued a famous "Ten Reasons" pamphlet arguing in favour of Catholicism.

When the pamphlet was distributed in Oxford, Campion became a wanted man. In July 1581, while preaching at Lyford Grange near Wantage, he was betrayed to armed constables. During the affray he managed to slip away - only to be discovered next morning when a priest-hunters pick drove through the wall of the secret cupboard in which he was hiding.

Taken to the Tower, Campion was tortured by thumbscrew, rack and more. When he and his comrades were eventually brought to trial and the rest held up their right hands as a sign of Not Guilty,' Campion could not do so, for his joints had been dislocated. Seeing this, a fellow prisoner, first kissing the maimed limb, raised it for him. Following a magnificent speech of defence Campion died on the gallows at Tyburn. When his body was cut down it was found that every nail had been torn from his fingers by his torturers.

A permanent exhibition at Stonor describes this grimly heroic chapter in the story of the house, and visitors can see the secret room, roof space and priest hole frequented by the martyr.

Stonor is open to the public in 2006 between April 2 -September 24. For further information visit call 01491 638587