For decades Sir Mark Rylance has been raising doubts over whether William Shakespeare wrote all the plays and poetry that bear his name.

Now the Oscar-winning actor has hit out at Stratfordians who dismiss his concerns, accusing them of “fearmongering” as he makes the case for why Sir Francis Bacon should be recognised as having made a major contribution to The Tempest and Love’s Labour’s Lost. In particular, he attacks the Shakespeare Birthplace Trust, the charity that oversees Shakespeare heritage sites in Stratford-upon-Avon.

In a foreword for a forthcoming book on the claims, Rylance writes: “Time will celebrate those who were not daunted by the fearmongering of the Shakespeare Birthplace Trust and its supporters in the media and academia.

“The Stratfordian response to our question about the authorship has usually been to lampoon the questioner. They can’t answer the question or make it go away, so they try to make us go away.”

Recalling that he was attacked when he first asked such questions, he says: “Now, 30 years on, I continue to be regularly and passionately attacked… for my doubt about the attribution of the works of Shakespeare to the uneducated man from Stratford-on-Avon.”

The book, Francis Bacon’s Contribution to Shakespeare: A New Attribution Method, argues that the statesman contributed to The Tempest and Love’s Labour’s Lost, among other works. Its author, Barry Clarke, believes his evidence moves “a single-author theory towards a many-hands theory”. Clarke has used computerised textual analysis to back up his theory. “A database called Early English Books Online has about 50,000 books before 1700, which are searchable. You can look up any phrase in these books. I went through The Tempest phrase by phrase and tried to figure out which phrases in the play were rare. Bacon is the only one who comes up for The Tempest. I did about 1,000 searches and there were about 13 rare phrase matches before and after The Tempest. When you’ve got mutual borrowing, it’s so unlikely that they borrowed from each other. It must be the same people.”

Shakespeare’s Birthplace, Stratford-upon-Avon. Photograph: VisitBritain

He compares, for example, “the print of good” (Bacon, Advancement of Learning, 1605), with the “print of goodness” (The Tempest, 1611), noting that the database search found only two out of 5,377 (0.037%) documents before 1611 for “print of good/goodness”.

Rylance was the first artistic director of Shakespeare’s Globe, and he recalls one newspaper describing him as a “heretic at the Globe” for suggesting Bacon’s authorship. In his foreword, he paraphrases Bacon in urging the public to read the book – “not to contradict and confute… but to weigh and consider”.

Since the 1850s, Bacon, Edward de Vere – the 17th Earl of Oxford – and Christopher Marlowe have been among dozens of candidates suggested as the likely single author. But, in 2013, in a publication titled Shakespeare Beyond Doubt: Evidence, Argument, Controversy, experts on Bacon, Oxford and Marlowe were among Shakespeareans who explained in a series of essays why only Shakespeare could have written his plays and poems, apart from his collaborations.

In his foreword, Rylance criticises a journalist who “demanded that I ‘come to my senses and accept that William Shakespeare the glover’s son’” was the author: “The journalist... claims I assert that a ‘posh boy’ must have done it.”

Class doesn’t come into it, he argues, but notes that, while there is no proof that Shakespeare attended any school, “his first plays, Love’s Labour’s Lost, for example, are full of university learning.”

He adds that Bacon “had the ability, the education, the wit and the life experience to write something like the Shakespeare works.”

Paul Edmondson, of the Shakespeare Birthplace Trust, said: “Readers might like to engage with the e-book ShakespeareBitesBack.Com, which discusses many of the salient points.”