Jonathan Caplan KC is a British barrister and King's Counsel who has studied UFOs for more than fifty years and served for many years on the editorial board of an international UFO journal. In June 2026 he published Not For Disclosure: UFOs: The World's Best Kept Secret, which argues that the United States and other governments have concealed recovered non-human craft for decades. The book's most striking claims, about presidents, intelligence agencies and contact events, are Caplan's own and rest largely on confidential sources and contested documents.

Called to the bar in 1973 and appointed Queen's Counsel in 1991, Caplan practises from 5 Paper Buildings in London in criminal and financial-fraud cases, extradition, regulatory work and media law. He has sat as a Recorder of the Crown Court, is a Bencher of Gray's Inn, and has tried cases in Hong Kong and Singapore. He represented Associated Newspapers at the Leveson Inquiry in 2012, and his clients have included Corinna zu Sayn-Wittgenstein-Sayn in her harassment claim against Spain's former king Juan Carlos and the widow of Lord Brittan after Operation Midland.

The book draws on interviews Caplan says he conducted over decades with researchers including Stanton Friedman, Jacques Vallée and Timothy Good, and on documents from a Majestic-12 archive that passed through researcher Tim Cooper and whose origin is disputed. Caplan argues that the papers match real meetings of President Truman and Defense Secretary James Forrestal in September 1947, while acknowledging that calendar entries cannot show what was discussed. He also writes that Edward Teller and three other Hungarian émigré scientists who jokingly called themselves "the Martians" later worked on Majestic projects.

Caplan promoted the book in Daily Mail essays and on GB News and NewsNation. In the Daily Mail and on Reality Check with Ross Coulthart, he tied the UFO secret to the CIA, to what President John F. Kennedy knew about UFOs before his death, and to Watergate. Those connections are his interpretation; no released official record has confirmed them. As reported by Liberation Times, he also writes that a CIA analytic unit has helped debunk the subject, that a few members of the congressional intelligence committees have been briefed on craft recoveries, and that in 1994 U.S. officials learned of a landing in Russia whose occupants met local militia. He has said that Prince Philip had people reporting alien encounters interviewed at Buckingham Palace, through his aide Sir Peter Horsley. Caplan says some of his sources cannot be named because of their official positions.

Caplan's standing as a senior criminal silk gave his book unusual mainstream reach in 2026 and made him one of the most prominent British voices in the renewed disclosure debate. Not For Disclosure is the work of a courtroom advocate assembling a cumulative case for official concealment, built largely from testimony and documents that no government has confirmed.