LONDON — Jailed for making false expense claims, Denis MacShane, a former British lawmaker, suffered another blow when he arrived last December at Belmarsh prison, a grim penitentiary in southeast London, and staff members confiscated the bag of books he had brought.

“You can’t take in that,” the prison officer said, Mr. MacShane recalled. When Mr. MacShane questioned the decision, the officer replied, “Don’t ask me; ask Chris Grayling.”

Mr. Grayling is Britain’s secretary of state for justice, and last November, his department tightened the rules on privileges granted to inmates. One of the changes was to restrict the flow of books into prisons, with a ban on packages of books brought or sent by friends and relatives. Mr. MacShane’s case suggests that some guards have interpreted the policy as a broader ban, though the Ministry of Justice says books should be confiscated only on admission for logistical reasons or if the books are considered inappropriate.

Either way, the effect is to move toward a system under which prisoners must borrow books from prison libraries or earn the right to buy them through good behavior.