LONDON — Fifteen-hour interrogations. Harmful cocktails of medicines. Offers of freedom in exchange for his theft of British government documents.

In his first public comments since being released last week from seven months of detention in the United Arab Emirates, Matthew Hedges, a British academic, described the extended psychological torture he says he endured at the hands of his interrogators.

Mr. Hedges, 31, was sentenced last month to life in prison after being convicted of spying for the British government during a research trip, part of his doctoral studies on the effects of the Arab Spring on Emirati diplomacy and security. He was pardoned by the Emirati government last week and returned to Britain after British officials lobbied for his release.

Locked up alone in a windowless cell with fluorescent lights that gave him migraines, Mr. Hedges was repeatedly accused by his captors of working for MI6, Britain’s foreign intelligence service and questioned about his sources for information that was freely available online, he said.