A vast number of essays and printed sermons on issues of religious controversy were produced by these radical clerics and their opponents over the following decades, in turn encouraging the further growth of the town's book trade.[14] The era also saw the birth of a Birmingham street literature, with broadside ballads on Birmingham subjects surviving from the middle years of the 17th century.[15] An Act of Parliament restricting the number of master printers in England meant that literature written and published in Birmingham could not be printed in the town, however, being produced only in London until the Act was repealed in 1693.[16]