A Territorial Army captain has resigned to publish a book critical of British actions in Afghanistan.
Mr Mike Martin said Nato troops in Helmand province “often made the conflict worse”.
He quit his role in the TA after the Ministry of Defence (MoD) refused to give him permission to publish the study.
An MoD spokesman said books by military personnel are “governed by well-established policy and regulations”.
Mr Martin studied Helmand for six years and completed an Army-funded PhD at King’s College in London.
He told the BBC Nato troops did not understand the “complexities” of Afghan tribal conflicts and were “manipulated” by tribal leaders fighting over land and water.
“This meant that we often made the conflict worse, rather than better,” he wrote in the study.
Mr Martin said he was originally told his final thesis could not be published as a book because it made use of secret cables published by Wikileaks and classified materials.
But he denied the book contained any intelligence material that was not in the public domain.
Last week, he was then told by his commanding officer that he was “not authorised to published the book”.
He resigned on Monday and will launch the book in London on Wednesdaynight.
The MoD said the department had accepted the material in the book did not contravene the Official Secrets Act.
But the book – An Intimate War – An Oral History of the Helmand Conflict 1978-2012 – had not been given official clearance, it added.
An MoD spokesman said: “The MoD has a strong record of learning from previous campaigns and encourages its officers to challenge existing norms and conventional wisdom.
“However the publication of books and articles by serving military personnel is governed by well-established policy and regulations. When these are breached the MoD will withhold approval.”