He was a prolific Elizabethan playwright who wrote the biggest hit of Shakespeare’s day, but the name of Thomas Middleton has been eclipsed for centuries by his contemporary.

Now new computer-assisted research concludes that hundreds of lines in Shakespeare’s Macbeth and Measure for Measure were written by Middleton, whose own plays about men and women pursuing each other, money, power and God drew huge audiences.

People have long recognised that both plays have passages uncharacteristic of Shakespeare, and suspected that Middleton had a hand in editing them after Shakespeare’s death. The terse style of Macbeth had been attributed to him. But the research goes much farther, saying that Middleton is “unmistakeably” the author of many more lines than previously realised – as much as 10 per cent of each play.

The evidence has been found both on stylistic grounds (a scientific study of words and phrases used elsewhere by Middleton but not by Shakespeare, such as “I believe thee” in Measure for Measure) and in references to historical events that took place after Shakespeare wrote the plays. Middleton’s contribution seems to be so extensive that both Macbeth and Measure for Measure are included in a new two-volume complete works of Middleton (1580-1627) by Oxford University Press (OUP).

Thomas Middleton: The Collected Works and Companion, which involved 75 scholars from a dozen countries, is published on November 22. It will be launched at Shakespeare’s Globe in London, near to where Middleton’s A Game at Chess, an allegorical satire attacking the Catholic Church and peace negotiations between England and Spain, packed the Globe playhouse in the 1620s.

Gary Taylor, Middleton’s joint general editor at OUP, said that the two Shakespeare plays would not have been included without compelling evidence. “What’s new is that we have greater confidence that it was Middleton. We can precisely identify which bits are Middleton.”

The Oxford Middleton provides evidence for the first time of lines that must have been written in 1616, the year of Shakespeare’s death, rather than in 1606, the year Macbeth was written. It singles out, for example, the scene in Macbeth between Lady Macduff, Ross and her son, just before the son’s murder. Elements such as perjury, remarriage, a mother whose husband is legally but not actually dead and a husband/father/Scot suspected of treason are linked in this research to the scandalous political trials associated with the murder of Sir Thomas Overbury in 1616. Middleton and Overbury were students together at Oxford and Middleton refers to the Overbury affair in several works.

The passage also echoes the circumstances of Middleton’s childhood. His father died when he was five, and his mother remarried, disastrously, less than ten months later. His stepfather left him and his mother to go abroad and was assumed to have died.

The revelation of the extent of Middleton’s involvement in rewriting Shakespeare comes 20 years after the Oxford Shakespeare acknowledged his collaboration on Timon of Athens.

Commenting on why Middleton has been overshadowed by his contemporary, Professor Taylor suggested it was partly because Shakespeare’s plays were published in 1623, just seven years after his death: “Middleton’s plays weren’t similarly collected . . . While Shakespeare’s company owned the legal right to have his plays printed, Middleton owned his own, and no one published one volume of his plays.

“That meant that, with the closing of the theatres in the Civil War, when they started up again following the Restoration, people only knew of three playwrights – Shakespeare, Ben Jonson and John Fletcher.” It was not until the 19th century that interest in Middleton was revived. By then, Professor Taylor said, “Shakespeare had more than a 200-year headstart”.

Stanley Wells, a Shakespeare scholar who contributed to the Middleton study, said that earlier claims that had relied on intuitive interpretation of the evidence had now been reinforced scientifically.

Toil and trouble: how the two writers square up

Middleton is said to have been responsible for these lines in Macbeth (from the scene between Lady Macduff, below, and her son): “Everyone that does so is a traitor and must be hanged” “And must they all be hanged that swear and lie”

Middleton’s own plays include lines such as: “Have ‘em all hanged up” “swear and lie”

Every word and phrase has been checked against databases of early modern English literature. This example shows phrases pointing to Middleton (who wrote elsewhere exact parallels for the idiom) rather than Shakespeare (who did not). Some phrases – such as “all . . . hanged” – occur in the work of no other Renaissance playwright

Changing of the Bard: how the writers square up

Thomas Middleton (1580-1627)
Author of The Changeling and The Revenger’s Tragedy In the early 1600s he became a “stagewright”, a profession held in no more esteem than acting, but he remained a “gentleman”, which was advertised on his title-pages His plays were performed for the Royal Court He was imprisoned in 1624 for his allegorical satire A Game at Chess. Though released, he apparently never wrote another play

William Shakespeare (1564-1616)
Author of 37 plays Left Stratford for London, but nothing is known of what he was doing before becoming a professional actor and dramatist in the capital In 1594, jointly formed a theatre company under the patronage of the Lord Chamberlain. For almost 20 years he was its regular dramatist, producing on average two plays a year

Source: OUP Middleton/ Shakespeare Birthplace Trust

Editor's choice

• U2 at Nou Camp Stadium, Barcelona
• The 50 Best Movie Villains
• The 15 golden rules of theatre etiquette