The British Guardian reports that 'black propaganda', issued by the British government, has helped to kill millions of people:

The British government ran a secret “black propaganda” campaign for decades, targeting Africa, the Middle East and parts of Asia with leaflets and reports from fake sources aimed at destabilising cold war enemies by encouraging racial tensions, sowing chaos, inciting violence and reinforcing anti-communist ideas, newly declassified documents have revealed.

The effort, run from the mid-1950s through to the late 70s by a unit in London that was part of the Foreign Office, was focused on cold war enemies such as the Soviet Union and China, leftwing liberation groups and leaders that the UK saw as threats to its interests

The campaign also sought to mobilise Muslims against Moscow, promoting greater religious conservatism and radical ideas. To appear authentic, documents encouraged hatred of Israel.

Recently declassified British government documents reveal hundreds of extensive and costly operations.

This isn't all new:

The Information Research Department (IRD) was set up by the post-second world war Labour government to counter Soviet propaganda attacks on Britain. Its activities mirrored the CIA’s cold war propaganda operations and the extensive efforts of the USSR and its satellites.

The Observer last year revealed the IRD’s major campaign in Indonesia in 1965 that helped encourage anti-communist massacres which left hundreds of thousands dead. There, the IRD prepared pamphlets purporting to be written by Indonesian patriots, but in fact were created by British propagandists, calling on Indonesians to eliminate the PKI, then the biggest communist party in the non-communist world.

To run such campaigns, by issuing false reports or publishing faked documents, does not require much staff:

The IRD employed 360 people at its height in the mid-60s. However, its highly secretive Special Editorial Unit, responsible for the black propaganda effort, was much smaller. From its base in a nondescript office in Westminster, the unit used a variety of tactics to manipulate opinion.

You can be assured that such efforts continue today:

Though the IRD was shut down in 1977, researchers are now finding evidence that similar efforts continued for almost another decade.

“The [new documents] are particularly significant as a precursor to more modern efforts of putting intelligence into the public domain.

“Liz Truss has a ’government information cell’, and defence intelligence sends out daily tweets to ‘pre-but’ Russian plots and gain the upper hand in the information war, but for much of the cold war the UK used far more devious means,” Cormac said.

More devious than falsely claiming that Iraq had weapons of mass destruction with the purpose of launching a war as the MI-6 did under its former directer Richard Dearlove?  More devious than running a 'Free Syrian Army' propaganda campaign as a cover for ruthless Jihadis? More devious than faking and promoting a 'dossiers' about the president of an allied country? More devious than running an Integrity Initiative to falsely propagandize Russia as an imminent danger to Europe?

I don't think so. Such stuff continues to this day and more is planned for the future.

For any nation the big dangers of such external operations is always that the same methods used in them can easily abused be for political purposes against internal 'enemies'.

Kit Klarenberg reports for the Grayzone that this is exactly what happened in Britain. Former MI-6 director Richard Dearlove and a few other insiders used leaks, false documents and propaganda to fire Prime Minister Theresa May and to install Boris Johnson in an effort to push for a hard Brexit:

Leaked emails and documents reviewed by The Grayzone have exposed the dimensions of a wide-ranging conspiracy managed by a shadowy cabal of hardcore Leavers to sabotage former Prime Minister Theresa May’s Brexit deal, remove her from office, replace her with Boris Johnson, and secure a ‘hard’ withdrawal from the EU.

The emails demonstrate that a group of operatives linked to the intelligence services and wealthy, reclusive pro-Brexit financiers spied on campaign groups, infiltrated the civil service, and targeted high-profile Remainers with reputational destruction. While the majority of British voters elected to assert their independence from the EU, this clique of mostly unknown influence agents sought to subvert the process and manage it according to their own elite interests.

Among their key objectives was to strengthen the security relationship between London and Washington, thus supplanting EU authority with more substantial US oversight.

The actors where all 'deep state' insiders:

The cabal appears to be led by Gwythian Prins, a member of the Chief of Defence Staff’s Strategy Advisory Panel, former NATO and Ministry of Defence advisor, and board member of pro-Brexit group Veterans for Britain. 

Prins’ bio on his speakers’ bureau advertises him as a “leading thinker on strategy” who has “worked with leading decision makers around the globe from business leaders all the way up to heads of state, helping them to improve their decision making by educating them on the complex psychological processes underpinning theses[sic] decisions.”

He is joined by former MI6 chief Richard Dearlove, who is frequently dubbed “C” in the leaked emails, a reference to the operational initial granted to all heads of Britain’s foreign intelligence service. At one point, Dearlove and Prins sought to recruit their apparent friend, Henry Kissinger, and his consulting firm as trans-Atlantic lobbyists for their version of Brexit.

These people are unscrupulous:

A leaked file authored in August 2018 by Prins spells out the cabal’s bold and malicious objectives in vivid detail. Motivated by a desire to “take the fight to our opponents, who are remorseless, by all necessary means,” its members sought to:

“Block any deal arising from the disastrous and craven Chequers White Paper; ensure that we leave on clean WTO [World Trade Organisation] terms; if necessary, remove this Prime Minister [emphasis added] and replace with one fit for purpose; cleanse the polluted civil service from top to bottom.”

Months later, in an email disseminating highly sensitive briefings for PM May on EU withdrawal, Prins instructed Dearlove: “Now kill her and it.”

The above named conspirators do not operate on their personal convictions but are mercenaries financed by shady billionaires:

Funding for what amounts to a covert political plot appears to have been furnished by wealthy backers including Tim and Mary Clode, an aristocratic husband and wife based in Jersey, a notorious British tax haven. 
…
Allegedly, Julian ‘Toby’ Blackwell, owner of the Blackwell publishing empire, also rustled up funds for the operation. An arch Brexiteer and multimillionaire who bankrolled numerous Leave entities, his Who’s Who entry lists his hobbies as “fighting Eurocrats and chopping firewood.”

The same people of course falsely claimed that the Brexit efforts the were secretly pushing were a 'Russian propaganda campaign'.

Britain is certainly not the only country where 'former' intelligence people secretly and openly run influence campaigns to push for certain policies. Just think of the 50+ former senior intelligence officers who falsely claimed that data from Hunter Biden's laptop was Russian disinformation.

I encourage everyone to read the Guardian piece and especially the the whole Grayzone piece and to judge on the evidence presented therein.