LONDON — The laptop — or what’s left of it — is a mangled carcass: Its innards have been ripped out, and only a few strips of metal and plastic remain. This was the MacBook Air that The Guardian used to store files leaked by the United States intelligence contractor Edward Snowden. Guardian employees destroyed the computer with power tools in July 2013 after the files on it were deemed a threat to British national security.

The destruction order came from the Government Communications Headquarters, or GCHQ, a 100-year-old intelligence and security agency tasked with keeping Britain safe. The organization, which usually prefers to be under the radar, is celebrating its centenary with “Top Secret: From Ciphers to Cyber Security,” an exhibition of more than 100 objects at the Science Museum in London that runs through Feb. 23.

In addition to the laptop, the items on show include an encryption key used by Queen Elizabeth II to make sure her phone conversations weren’t tapped and a briefcase containing a clunky brown handset that Prime Minister Margaret Thatcher used for top-secret calls.

GCHQ is one of Britain’s most secret and secretive organizations: It wasn’t officially acknowledged in law until 1994. So why has it decided to appear in a London museum?