A British scholar and former university lecturer, Brenda James, and a historian, Professor William Rubinstein, of the University of Wales, Aberystwyth, are proposing that the real Shakespeare was an English courtier and diplomat called Sir Henry Neville.

The issue of who wrote the body of works attributed to William Shakespeare has been hotly debated by academics for centuries. There has always a suspicion that Shakespeare, the grammar school-educated son of a Warwickshire alderman, who failed to progress to either Oxford or Cambridge universities, could not have possessed the learning or wit to produce plays such as Hamlet, King Lear and Twelfth Night.

Literary rivals including Ben Jonson, Francis Bacon and Christopher Marlowe, assorted nobles such as the earls of Oxford, Essex and Southampton, and even the maritime adventurer Sir Walter Raleigh have all been named as the real executors of the classic texts.

But the new suggestion is backed by a vast amount of startling evidence suggesting that Neville, a man never before associated with the mystery, wrote all the plays attributed to Shakespeare. The claims will be published in a book due to be launched this month at Shakespeare's Globe theatre in London by its artistic director, the actor Mark Rylance.

The political content and geographical location of the plays are a perfect reflection of the known travels of Neville, a highly educated diplomat and politician who lived from 1562 to 1615 and came from Berkshire. Shakespeare lived from 1564 to 1616.

The authors have meticulously traced connections between Neville's travels abroad and the Shakespeare corpus. For example, between 1599 and 1600, he briefly became ambassador to France, leading, it is claimed, to the writing of Henry V, in which some scenes were written in French, a language Shakespeare did not speak.

As a politician, Neville became involved in an unsuccessful revolt led by the Earl of Essex against the government in 1601. Neville was imprisoned in the Tower of London for treason - hence the shift in tone of the plays, which changed abruptly from being mainly historical or comic to being predominantly sombre and tragic.

The plays also portray many of Neville's royal and other ancestors - John of Gaunt in Richard II, Warwick the kingmaker in Henry VI, Part II and King Duncan of Scotland in Macbeth - in a particularly favourable light.

A further piece of evidence is a document, now known to have been written by Neville while he was a prisoner in the Tower, which contains detailed notes, the contents of which ended up being used in Henry VIII.

There are also striking similarities of style and vocabulary between Neville's private and diplomatic letters and the Shakespeare plays and poems. In addition, word frequency analysis reveals a statistical correlation. Finally, the authors claim to present direct but long-ignored evidence, in a document discovered in 1867, that Neville practised faking William Shakespeare's signature. The document, in Neville's handwriting and with his name at the top, features 17 attempts at practising various forms of Shakespeare's signature.

The two scholars propose that Shakespeare was Neville's "front man" , suggesting that the diplomat could not afford to be seen as the author of the plays because some of them were too politically sensitive and controversial. Indeed, if the Elizabethan authorities had known that Neville was the author of Richard II, he would probably have been executed rather than merely imprisoned after the Earl of Essex's revolt in 1601.

Neville's fundamental political problem was that he was a member of a rival dynasty to that of the Tudors. He was descended from the Plantagenets. His own grandfather and great uncle had been executed by Henry VIII. Richard II, which deals with the forcible deposition of a monarch, was performed in London 40 times just before Essex's revolt - and was regarded by the authorities as seditious. Shakespeare and his colleagues were questioned by government investigators, but were not arrested.

One of the few documents officially attributing the plays to Shakespeare was the First Folio edition, published in 1623. The writer Ben Jonson was involved in putting Shakespeare's name on that first edition and, at the time , he was employed by a college in London associated with the Neville family. Ms James and Professor Rubinstein believe that Jonson knew about the "front-man" arrangement and helped promote the fiction of Shakespeare's authorship at the behest of the Neville family - presumably out of respect for Henry Neville's wishes.

With such politically controversial ancestry, Neville couldn't afford to be seen writing politically controversial plays. Ms James and Professor Rubinstein also suggest that the character Falstaff - who appears in four plays - was actually based on Neville himself. Falstaff was initially going to be called "Oldcastle", an antonymic pun on Neville's name (derived, as it was, from the French "New Town").

Significantly, Shakespeare's patron was the Earl of Southampton, who was one of Neville's closest associates. Furthermore, Shakespeare's mother, Mary Arden, was a relative of Neville. It is through these two connections that Ms James and Professor Rubinstein suggest Neville met Shakespeare, and proposed Shakespeare become his front man.

Scholars have always been puzzled as to how William Shakespeare wrote plays requiring detailed geographical and political knowledge and advanced skills in reading Latin, Greek, French, Spanish and Italian textual sources - yet ceased his formal education at the age of 12.

"We have amassed such a huge body of new evidence that the case for Neville being the true author of the Shakespeare plays seems overwhelmingly strong," said Professor Rubinstein. "We correlated the chronology of the plays with Neville's life and found that they match perfectly in a way that illuminates the evolution of the plays."

Brenda James added: "The beauty and eloquence demonstrated in Neville's diplomatic and personal letters display a linguistic liveliness and inventiveness that is echoed boldly in the works attributed to Shakespeare. Examining his letters I have found examples of particular unusual words and constructions not normally found outside Shakespearean literature."

The Truth Will Out is published on 25 October

The clues

* Love's Labour's Lost echoes in part the issues discussed specifically at Oxford University at the time that Neville was studying there between 1574 and 1579. Many characters in the play were known personally to Neville.

* Measure for Measure was set in Vienna, which Neville visited in 1580. A theme of the play - laws against immorality - reflects specific ideas Neville encountered when he met a Calvinist philosopher there.

* Romeo and Juliet, The Taming of the Shrew, Two Gentleman of Verona, and The Merchant of Venice were all set in northern Italy, which Neville visited in 1581 and 1582.

* Hamlet was set in Denmark, and, according to James' research, Neville obtained specific information on the background to Hamlet while visiting what is now Poland, and possibly Denmark itself .

* Henry V reflects Neville's journey to France, where he became English ambassador in 1599-1600. Some of its scenes were actually written in French, which Neville spoke but Shakespeare did not. And in Henry IV, Part II, written just before Neville went to France, a character speaking towards the end of the play actually says: "I have heard a bird sing" that "we will bear our civil swords" to France .

The other theories

FRANCIS BACON

This theory appears to have emerged in the 19th century, based on textual comparisons between Bacon's known writings and the plays. A common piece of evidence cited is the "nonsense" word found in Love's Labour's Lost - "honorificabilitudinitatibus". It is claimed that this is an anagram: "hi ludi F.Baconis nati tuiti orbi" or "these plays born of F Bacon are preserved for the world". But the word is the dative singular conjugation of a real medieval word, so it does not have to be code for anything else. Twentieth- century analysts have dismissed the Bacon claim.

EDWARD DE VERE, THE 17TH EARL OF OXFORD

The evidence is circumstantial in that Oxford's known poems apparently ceased just before Shakespeare's work began to appear. The argument is that Oxford assumed a pseudonym to protect his family from the embarrassment of being associated with the stage.

CHRISTOPHER MARLOWE

One of the more extravagant theories in that it claims Marlowe was not killed in a tavern brawl in 1593, but was smuggled to France and then Italy, where he continued to write in exile in a new style. The works were then allegedly attributed to Shakespeare, who was paid to keep silent.

WILLIAM STANLEY, 6TH EARL OF DERBY

A keen theatre enthusiast, he was patron of his own company of actors. Several poems written in the 1580s in an immature Shakespearean style, but not believed to have been by Shakespeare himself, are signed W.S. and one is in Derby's handwriting. It is conjectured that to conceal Derby's identity, W.S. for William Stanley was expanded to William Shakespeare.