Sometimes, the analysis of metadata is shared between allied services, current and retired U.S. intelligence officers say. This is particularly true with the GCHQ, Britain’s equivalent of the NSA.

One former senior U.S. intelligence official with knowledge of the program tells The Daily Beast, “My understanding is if the British had a phone number, we might run the number through the database for them and provide them with the results.”

“I do not know of cases where the U.S. government has shared this kind of metadata with the United Kingdom, but I would be surprised if this never happened,” Wood says. “Both countries cooperate very closely on counterterrorism.”

The U.S. and the U.K. have an agreement to share signal intercepts and electronic intelligence through a pact known as the United Kingdom United States of America Agreement. Over the years, the agreement has been expanded to include Australia, Canada, and New Zealand.