Secrets, spy tools and a 110-year-old lemon are on show in an exhibition from Britain's MI5

LONDON (AP) — A desiccated 110-year-old lemon that played a key role in espionage history is one of the star attractions of a London exhibition drawn from the files of MI5, Britain’s domestic intelligence agency.

Compact spy cameras, microdots in a talcum powder tin and a briefcase abandoned by fleeing Soviet spy Guy Burgess are also part of the show at Britain’s National Archives, which charts the history of a secretive agency that is – slowly – becoming more open.

MI5 Director General Ken McCallum told journalists at a preview on Tuesday that the organization’s work “is often different from fiction, whether that fiction is George Smiley or Jackson Lamb” – the brilliant spymaster of John le Carré's novels and the slovenly supervisor of MI5 rejects in Mick Herron’s “Slow Horses” series.

Many stories told in the exhibition, however, would not be out of place in a thriller.

The lemon, now black and shriveled, helped convict Karl Muller, a German spy in Britain during World War I. It was found by police in his dressing-table drawer, along with another in his overcoat pocket. Evidence at his secret trial showed their juice had been used to write invisible-ink letters detailing British troop movements.

Muller was executed by firing squad at the Tower of London in 1915.

In a coda that would not be out of place in “Slow Horses,” MI5 pretended Muller was still alive and wrote to his German handlers to ask for more money.

“The Germans duly sent more funds and MI5 used the funds to purchase a car,” exhibition curator Mark Dunton said. “And they christened the car ‘The Muller.’

“They then were reprimanded by the Treasury for unauthorized use of expenditure," he added.

The show includes declassified records held by the National Archives and items loaned from the secret museum inside Thames House, MI5’s London headquarters.

It charts the changing role of an agency that was founded in 1909 as the Secret Service Bureau with an initial staff of two officers.

There are records of its World War II successes, when the agency used captured Nazi agents to send disinformation back to Germany, deceiving Adolf Hitler about the location of the looming Allied invasion in 1944.

Failures include the years-long betrayal of the upper-crust “Cambridge Spies,” whose members spilled secrets to the Soviet Union from the heart of the U.K. intelligence establishment. Recently declassified MI5 documents on display include the 1963 confession of Cambridge spy Kim Philby, who denied treachery for years before he was exposed and fled to Moscow.

The exhibition also reveals changing attitudes, not least to women. The exhibition includes a 1945 report by spymaster Maxwell Knight discussing whether women could make good agents.

“It is frequently alleged that women are less discreet than men,” he noted, but declared that it was not so, saying that in “hundreds of cases of ‘loose talk’” most of the offenders were men.

There are admissions of past mistakes. The exhibition notes that MI5 was slow to recognize the threat from fascism in the 1930s, and later spent too much time spying on the small Communist Party of Great Britain. MI5 didn’t need to break into the party’s offices – it had a key, which is on display.

There are only a few items from the past few decades, showing how MI5’s focus has shifted from counterespionage to counterterrorism. Displays include a mortar shell fired by the Irish Republican Army at 10 Downing St. in 1991 while Prime Minister John Major was holding a Cabinet meeting.

MI5 only began releasing records to the U.K.’s public archives in 1997, generally 50 years after the events have passed. Even now, it controls what to release and what to keep secret.

“It would be a mistake to assume everything is in the exhibition,” said author Ben Macintyre, whose books on the history of intelligence include “Operation Mincemeat” and “Agent Zigzag.” But he said it still marks “a real sea-change in official secrecy.”

“A generation ago, this stuff was totally secret,” he said. “We weren’t even allowed to know that MI5 existed.”

“MI5: Official Secrets” opens Saturday and runs through Sept. 28 at the National Archives in London. Admission is free.

A National Archives staff member looks at a 1910 Enseignette camera, the first spy camera purchased by MI5, during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

A Yardley talcum powder tin from 1960 used by one of the Portland spies to conceal microdot equipment on display during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

The Krogers' 'flash transmission' radio equipment, 1960, on display during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

The lemon used for writing in invisible ink, produced in evidence at Karl Muller's trial, 1915, on display during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

A copy of the German War Merit Cross 'Kriegsverdienstkreuz', 1939 on display during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

MI5 staff list on display during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

Director General of MI5, the UK's Security Service, Ken McCallum, during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

A National Archives staff member looks at an example of an instant camera and bottle used to make a bomb, recreated as evidence by the Bomb Data Centre, on display during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

Guy Burgess' passport on display during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

EA National Archives member of staff looks at a Britain First report of Mosley's speech at Earl's Court, 16 July 1939, left, and a British Union of Fascists armband, right, during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

National Archives staff members look at facets of a recreation of the double cross operation room which was headed up by the XX committee circa 1944, during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

Director General of MI5, the UK's Security Service, Ken McCallum, during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

National Archives staff members look at facets of a recreation of the double cross operation room which was headed up by the XX committee circa 1944, during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

Guy Burgess' passport and briefcase on display during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

National Archives staff members look at facets of a recreation of the double cross operation room which was headed up by the XX committee circa 1944, during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP)

ADEN, Yemen (AP) — Saudi warplanes have reportedly struck on Friday forces in southern Yemen backed by the United Arab Emirates, a separatist leader says.

This comes as a Saudi-led operation attempts to take over camps of the Southern Transitional Council, or STC, in the governorate of Haramout that borders Saudi Arabia.

Tensions between Saudi Arabia and the UAE rose after the STC moved last month into Yemen’s governorates of Hadramout and Mahra and seized an oil-rich region. The move pushed out forces affiliated with the Saudi-backed National Shield Forces, a group aligned with the coalition in fighting the Iran-backed Houthis in Yemen.

Meanwhile, the Saudi ambassador to Yemen accused the head of the STC of blocking a Saudi mediation delegation from landing in the southern city of Aden.

The STC deputy and former Hamdrmout governor, Ahmed bin Breik, said in a statement that the Saudi-backed National Shield Forces advanced toward the camps, but the separatists refused to withdraw, apparently leading to the airstrikes.

Mohamed al-Nakib, spokesperson for the STC-backed Southern Shield Forces, also known as Dera Al-Janoub, said Saudi airstrikes caused fatalities, without providing details. The Associated Press couldn’t independently verify that claim.

Al-Nakib also accused Saudi Arabia in a video on X of using “Muslim Brotherhood and al-Qaeda militias” in a "large-scale attack " early Friday that he claimed sepratists were able to repel.

He likened the latest developments to Yemen’s 1994 civil war, “except that this time it is under the cover of Saudi aviation operations.”

Salem al-Khanbashi, the governor of Hadramout who was chosen Friday by Yemen's internationally recognized government to command the Saudi-led forces in the governorate, refuted STC claims, calling them “ridiculous” and showing intentions of escalation instead of a peaceful handover, according Okaz newspaper, which is aligned with the Saudi government.

Earlier on Friday, al-khanbashi called the current operation of retrieving seized areas “peaceful.”

“This operation is not a declaration of war and does not seek escalation,” al-Khanbashi said in a speech aired on state media. “This is a responsible pre-emptive measure to remove weapons and prevent chaos and the camps from being used to undermine the security in Hadramout,” he added.

The Saudi-led coalition in Yemen demands the withdrawal of STC forces from the two governorates as part of de-escalation efforts. The STC has so far refused to hand over its weapons and camps.

The coalition's spokesperson Brig. Gen. Turki al-Maliki said Friday on X that Saudi-backed naval forces were deployed across the Arabian Sea to carry out inspections and combat smuggling.

In his post on X, the Saudi ambassador to Yemen, Mohammed al-Jaber, said the kingdom had tried “all efforts with STC” for weeks "to stop the escalation" and to urge the separatists to leave Hadramout and Mahra, only to be faced with “continued intransigence and rejection from Aidarous al-Zubaidi," the STC head.

Al-Jaber said the latest development was not permitting the Saudi delegation's jet to land in Aden, despite having agreed on its arrival with some STC leaders to find a solution that serves “everyone and the public interest.”

Yemen’s transport ministry, aligned with STC, said Saudi Arabia imposed on Thursday requirements mandating that flights to and from Aden International Airport undergo inspection in Jeddah. The ministry expressed “shock” and denounced the decision. There was no confirmation from Saudi authorities.

ِA spokesperson with the transport ministry told the AP late Thursday that all flights from and to the UAE were suspended until Saudi Arabia reverses these reported measures.

Yemen has been engulfed in a civil war for more than a decade, with the Houthis controlling much of the northern regions, while a Saudi-UAE-backed coalition supports the internationally recognized government in the south. However, the UAE also helps the southern separatists who call for South Yemen to secede once again from Yemen. Those aligned with the council have increasingly flown the flag of South Yemen, which was a separate country from 1967-1990.

—

Associated Press writers Bassem Mroue in Beirut and Fatma Khaled in Cairo contributed to this report.

Southern Yemen soldiers of Southern Transitional Council (STC) at a check point, in Aden, Yemen, Wednesday, Dec. 31, 2025. (AP Photo)