It has thrills, spills, sword fights, violent sexual assault and – to modern ears – a terrible ending, but the little-known 18th century play Double Falsehood was propelled into the literary limelight today when it was claimed as a lost Shakespeare.

Professor Brean Hammond of Nottingham University will publish compelling new evidence next week that the play, a romantic tragi-comedy by Lewis Theobald is – as the author always maintained it was – substantially based on a real Shakespeare play called Cardenio.

Hammond has been backed in his assertion by the Shakespeare publisher Arden and there are unconfirmed rumours that the play will open at the Royal Shakespeare Company's Swan Theatre in Stratford when the venue reopens after its three-year closure.

The claim represents 10 years of literary detective work by Hammond. "I don't think you can ever be absolutely 100% but, yes, I am convinced that it is Shakespeare," he said. "It's fair to say it's been something of an obsession. You need to ask my wife but a fair few of my waking hours have been devoted to this subject."

Theobald's Double Falsehood, or The Distrest Lovers was first performed in 1727 at the Drury Lane theatre in London, along with the remarkable claim that it was based on Shakespeare's "lost play" Cardenio, which was first performed in 1613. Theobald claimed to have three original texts of Cardenio.

Double Falsehood went down well with audiences, but it was badly received by expert observers who dismissed Theobald as a hoaxer. Alexander Pope, in particular, was scornful but the two were committed enemies. "Theobald was the author of a volume in 1726 called Shakespeare Restored which was a hatchet job on Pope's editing of Hamlet," said Hammond. "In that volume Theobald made it pretty clear that he considered himself superior to Pope."

The denunciation became accepted as fact: Theobald was little more than a hoaxer, albeit an audacious one. The play then went largely to ground apart from a performance in 1846 when – after the audience shouted "author? author?" – a plaster bust of Shakespeare was brought out. It was laughed off stage.

The play reads like Shakespeare, but reworked Shakespeare. Hammond called Double Falsehood a "flawed play", adding: "This version of the Shakespeare play has been doctored. Theobald cut out material that he didn't think appropriate, but this was quite common. Shakespeare was very frequently rewritten in the 17th and 18th centuries."

The play is much shorter and more bitty than a normal Shakespeare play and there are no long speeches. But there is plenty of action that centres on two men and two women, including an aristocratic villain called Henriquez who ravishes the virtuous young girl Violante. By the end he has repented and is strikingly forgiven by all.

The Arden Shakespeare's general editor, Richard Proudfoot, said the play was being made accessible for the first time in 250 years. "I think Brean Hammond's detective work has been superb. He is quite open to the obvious fact that there is an element of speculation, but both of us believe that the balance of doubt lies in favour of its claim being authentic rather than a total fabrication."

Over the years some 77 plays have been attributed in whole or in part to Shakespeare, about half of them wrongly. There are also plenty of theories and books published claiming Shakespeare's plays were written by Edward de Vere, Sir Francis Bacon or Christopher Marlowe.

Act 2, scene 1 of Double Falsehood

Lopez [to Fabian]: Soft, soft you, neighbour; who comes here? Pray you, slink aside. [They withdraw.]

Henriquez: Ha! Is it come to this? O the devil, the devil, the devil!

Fabian [to Lopez]: Lo you now, for want of the discreet ladle of a cool understanding will this fellow's brains boil over!

Henriquez: To have enjoy'd her, I would have given – what?

All that at present I could boast my own,

And the reversion of the world to boot

Had the inheritance been mine. And now –

Just doom of guilty joys! – I grieve as much

That I have rifled all the stores of beauty,

Those charms of innocence and artless love,

As just before I was devour'd with sorrow,

That she refus'd my vows and shut the door

Upon my ardent longings.

Lopez [to Fabian]: Love! Love! Downright love! I see by the foolishness of it.