John Dee is commonly regarded as England's finest home-grown magus, our most notable exponent of the esoteric arts that promised astonishing advances in knowledge for 16th-century Europe. His name is mentioned along with those of Paracelsus and Giordano Bruno, and he is sometimes proposed as an inspiration for Dr Faustus, Prospero or Ben Jonson's Alchemist.

Usually he is imagined as a secretive, reclusive figure, studying in the great library he assembled at his house at Mortlake, or absorbed in mercurial experiments in his laboratories there. But now Glyn Parry suggests that Dee was actively involved in affairs of state, frequently consulted by influential politicians and courtiers, and had a connection to Queen Elizabeth herself.

Dee's patrons were the great men of state: William Cecil, later Lord Burghley, who was the queen's chief minister; the earls of Warwick and Pembroke; and the queen's favourite, the Earl of Leicester. He had close relations with Sir Philip Sidney, Sir Walter Raleigh and Sir Francis Walsingham. All these men appear to have had a serious interest in alchemy and astrology, and it is Parry's intention to show that magical practices permeated political and social life in later Tudor England, and that the currency of such practices has been largely overlooked.

Certainly, the belief that knowledge and power could be enlarged by celestial assistance was ingrained in the mentality of the age. When Mary Tudor was thought to be pregnant, Dee was casting horoscopes for her, her husband Philip of Spain and for Princess Elizabeth to predict the consequences. Would Mary live? Would Elizabeth succeed? What would be the fate of Philip? How long would the protagonists live? While such information would be invaluable to politicians, occult delving into matters of state could result in prosecution.

It was widely believed that the alchemical quest would lead to the attainment of the philosophers' stone. The "stone" was thought to be a powder that would aid in the transmutation of ignoble metals into gold, while the "great elixir" that would be created in the final passages of the quest would cure all disease and be an antidote to corruption. The processes of alchemy required the co-operation of the stars, and on occasion, the aid of spirits. The ministers of state desperately needed gold to enlarge the navy, maintain the war against Spain in the Low Countries, support the expeditions to Ireland and develop a British empire  a phrase coined by Dee. Success in alchemy would be the answer to their prayers.

Elizabeth herself may have been drawn in to this quest, sometimes with Dee as a consultant. Parry claims that she keenly believed in the possibilities of transmutation and had her own laboratories at Hampton Court, where she maintained her own alchemist on a substantial pension. He offers us a seductive "vision of her moving restlessly among her alembics  endlessly seeking the elixir". The evidence, however, is always oblique.

Increasingly, Dee looked for assistance from spirits. His communication with angels, recorded in great detail and eventually published in one of the truly enigmatic books of the 17th century, probably began as an aid to his alchemy, but it developed into prophecy and prediction. The presence of angels was universally acknowledged, but those who invoked them ran the risk of being accused of witchcraft, for there were good angels and bad angels.

Dee assured himself he was dealing with virtuous spirits. He contacted them by means of a crystal ball and a highly polished obsidian disc (both of which are now in the British Museum), employing a medium, Edward Kelley, to interpret the angels' language and their semi-coherent messages. Many of their transmissions were related to the phenomena of the latter days of the world: wars and rumours of wars, and the rise of a universal emperor who would purge corruption in church and state, and unify divided Christendom.

The most intense angelic conversations took place in eastern Europe, for Dee was in demand internationally. He went to Poland, invited by an aristocrat who had his eye on the throne, and needed gold and angelic advice. He moved on to Prague, where he failed to persuade the Emperor Rudolph of the authenticity of his prophecies.

We too may have our doubts, and Parry himself is never explicit about his own views on the credibility of Dee's activities. Suspicion of the "arch-conjurer" deepened in England, where he fell foul of the church establishment, which was beginning to crack down on magical practices, and Dee was increasingly suspected of witchcraft.

In this intensively researched book, we are invited to imagine Elizabethan England as a much stranger place than we had assumed. John Dee comes across as a figure of national significance in an age with a belief system very different from ours. His dark arts promised much, yet delivered little, and finally brought him into disrepute.

 Graham Parry's Glory, Laud and Honour is published by Boydell Press.