NEWLY published letters by Charles Wesley, the co-founder of the Methodist movement, suggest that the extravagant habits of his wife, Sally, were a constant source of tension between them. And close examination of 700 letters from Wesley suggests that some of his earnings from the hymns he wrote were used to pay for her luxury lifestyle.

The details are disclosed in The Letters of Charles Wesley: A critical edition, by Dr Gareth Lloyd, of the University of Manchester, and Professor Kenneth Newport, the Pro Vice-Chancellor of Liverpool Hope University. They are among a handful of people who are capable of transcribing Wesley's personal shorthand, comprised of a mixture of Latin, Greek, and Hebrew.

When Wesley married Sally Gwynne, 19 years his junior, he promised her parents that he would keep their daughter "in the manner to which she was accustomed". Dr Lloyd says: "Charles Wesley effectively married above himself. His wife came from a wealthy Welsh family, and his future father-in-law was a sheriff of the county and a large landowner.

"Her friends came from higher ranks of society, and she would entertain them with parties and soirées. They obviously weren't entertaining on a vast scale, but if you were inviting your aristocratic friends around to tea, there were obviously certain standards that needed to be maintained, so that caused some grievance.

"Wesley came from a family where there wasn't a great deal of money; so he was maybe a bit paranoid about it. He told his children that she was a poor manager of money. He was worried about whether they would be able to pay the bills." In one letter to his daughter Sarah - who, like her mother, was also known as Sally - in August 1787, Wesley suggested that money was "a difficulty that never comes into your mother's head".

The situation led to friction between Wesley and his brother John, co-founder of the movement, when he asked if profits from the sale of hymn books could be diverted to fund his wife. Dr Lloyd says that the money became a "bone of contention" between the brothers in later years, as John accused Charles of profiting.

Professor Newport says: "These letters . . . show Wesley as a devoted, but sometimes rather puzzled, family man who struggled at times to curb his young wife's extravagance."

The two academics have spent a decade working on the letters, which were written between 1727 and 1788, the year of Wesley's death. "Wesley's genius as a preacher and religious leader contributed to the birth of the evangelical movement, probably the greatest success story of the modern Church," Dr Lloyd says. "His life and ministry, even within Methodism, have received scant attention; so we are pleased that this collection will change that."