Long-forgotten documents revealing how William Shakespeare’s entrepreneur father John was victimised by informers who wanted to extract money from him have been discovered in the depths of the UK’s National Archives.

Depicting events which are believed to have shaped the teenage Shakespeare’s attitude to power and morality, later explored in plays from King Lear to Macbeth, the 21 previously unknown documents were discovered by Professor Glyn Parry from the University of Roehampton, and are “of the utmost importance” to our understanding of the playwright, according to the National Archives’ head of early modern records, Dr Katy Mair.

Although William Shakespeare’s baptism is recorded in April 1564, and his marriage in December 1582, further details of the playwright’s early life have had to be gleaned from records of his father John Shakespeare’s colourful career, with previously uncovered manuscripts revealing that John had been accused of illegal moneylending and wool-dealing by professional informers between 1569 and 1572. Scholars have assumed the cases were settled out of court by 1573, but the newly found documents show that John – whose lines of work stretched from glover and leather maker to alderman, magistrate and more – was in financial and legal trouble until around 1583, when William was 19.

Writ of attachias to the Sheriff of Warwickshire to seize [the goods and chattels of] John ‘Shakespere’ of Stratford upon Avon. Photograph: Crown Copyright, courtesy of The National Archives

Parry, who is co-writing a book about Shakespeare’s life up until 1592, said that until he began digging into the National Archives, 150 years of research had produced fewer than 15 documents relating to John Shakespeare. He was “not happy” with the story that John had settled his prosecution for usury and wool-dealing out of court, around 1573, so delved into the National Archives’ list of Exchequer documents.

He began ordering boxes of documents down from the salt mines in Cheshire where little-used papers are sent for safe-keeping, and started going through the writs for Warwickshire, beginning with the dates of John’s court cases.

“I had identified just over 100 possible boxes, and inside each box there could be between 100 and 1,000 writs and associated documents, depending on how many had survived,” he said. “Quite quickly I turned up one writ, then more, working through May into early June. In August I found more … It was very exciting to have an educated hunch pay off, which is quite rare when working in the less-used parts of any archive. It’s a bit like that Christmas morning feeling as a child, unwrapping the box and finding the perfect, longed-for present.”

The documents Parry found include multiple writs against John Shakespeare, and record his debts to the Crown, including one for £132 – around £20,000 today. They reveal how his property remained at risk of seizure by the Crown, hampering his credit as an entrepreneur, and that this continued until 1583.

Undercover work … some of the many thousands of documents stored in a Cheshire salt mine. Photograph: Graeme Robertson/The Guardian

John Shakespeare fell victim to a perfectly legal kind of persecution. William grew to adulthood in a household that had been 'downranked'

They also connect Shakespeare’s family with what Parry calls “a national scandal: the use of informers to enforce economic and social legislation”. Professional informers were part of a corrupt system which ultimately enriched the Queen and her courtiers. “A lot of people grumbled but settled. For some reason in two cases John Shakespeare did not, and ended up targeted by the Exchequer collection system, which damaged his local credit. If he bought wool on credit to sell for cash the wool might be seized by the Crown. If people borrowed money from him that debt could also be seized by the Crown, which had much more aggressive collection methods than John Shakespeare,” said Parry.

“So John Shakespeare fell victim to a perfectly legal kind of persecution, which ruined his business through the 1570s, and William grew to adulthood in a household where his father had fallen in social and economic rank, which sociologists and psychologists tell us leads to anger. They call it ‘downranking’. Again, it was all according to the letter of the law. It was just unjust if you were on the receiving end.”

Parry believes that the situation would have influenced the teenage Shakespeare’s attitude to “power politics”, particularly when coupled with his schooling; it is believed that he studied Latin texts by Ovid, Horace, Livy and Tacitus while at Stratford Grammar School. The Roman authors “mourned the loss of republican virtues and the moral decline of political life under the emperors”; combined with his difficult family life, this would have all “informed his political outlook, a sceptical sideways look at power and its pretensions,” said Parry.

Sense of place … John Shakespeare’s business troubles must have overshadowed his son’s early life. Photograph: Graeme Robertson/The Guardian

“William Shakespeare learned in the schoolroom what he experienced at home, that, under monarchy, men who served the monarch immorally could flourish. There’s a deep desire for justice and equity, not the strict letter of the law, that runs through all his writing, and a critical view of the pretensions of the mighty.”

The academic says he has “no doubt” that there are more Shakespeare materials to be found in the National Archives, many parts of which have no detailed catalogues, lists or indexes, and he intends to keep looking.

Mair said: “It is often believed that there are no new documents relating to Shakespeare left to be found, but Professor Parry has shown that there are still discoveries waiting to be made here in the reading rooms at the National Archives.”

Parry’s findings will be included in Shakespeare Documented, an online collection of primary-source materials about the life of William Shakespeare.