Here's a fun fact for anyone who enjoys both universal healthcare and historical irony: Aneurin "Nye" Bevan, the man who founded the NHS, was spied on by MI5 for more than 20 years. Newly released files given to the National Archives show that the security service first took an interest in the Welsh MP from Tredegar, Blaenau Gwent, back in the 1930s, when he was considered a firebrand left-winger with prominent communist connections.

Monitoring continued even after Bevan became a minister in the post-war Labour government and drove through the creation of the NHS despite fierce opposition from doctors. Because nothing says "national security threat" like guaranteeing people medical care.

At one stage, the then MI5 director general became so concerned about Bevan's links to a Russian spy that he went to see Prime Minister Clement Attlee in No 10 to warn him. One imagines the meeting was tense, at least until someone pointed out that Bevan's activities were, in fact, entirely public.

Indeed, some within MI5 questioned why the service was bothering at all, given that everything Bevan did was in the open. After his death in 1960, one MI5 officer described the content of the file as "remarkably tame." A ringing endorsement of two decades of surveillance.

The papers show MI5 first opened a file on Bevan in 1933, when he was backbench Labour MP for Ebbw Vale. One of the earliest reports included an account of an anti-Nazi rally in Montreal, Canada, which Bevan addressed in 1934. "Bevan has inherited the evangelical fervour of his Welsh forebears and knows how to use it in the Communist cause," it read, presumably with a straight face.

In 1943, Roger Hollis, the future director general, summarised what they knew of Bevan's activities. In 1933, he said the MP had been "in close touch" with Communist Party of Great Britain general secretary Harry Pollitt and party members who backed his plan to organise "workers' freedom groups" to defend against "capitalists." Nothing in the files suggests MI5 tapped his phone or intercepted his mail, but some officers still wondered why they were watching him at all. "I do not think that Bevan's activities are a matter in which we, the security service, should be involved," one officer wrote in 1943. "In fact he makes exactly the same remarks in the Houses of Parliament pretty frequently."

The reporting continued after the war when Bevan was made health minister in Attlee's government. In 1949, MI5 became increasingly concerned about Bevan's friendship with Wilfred Macartney, described in the files as "an unsavoury, unscrupulous character" convicted of spying for Russia in 1928. Recordings of conversations suggested Macartney was passing information obtained by Bevan to Communist Party leader Pollitt. That May, MI5 chief Sir Percy Sillitoe took evidence to Attlee, who dismissed Macartney's claims as a "tissue of lies" but agreed to warn Bevan about him.

One of the final reports dates from 1954, when Bevan, now back in opposition, was invited to meet Soviet ambassador Yakov Malik at London's Polish embassy. The event "went off very badly," partly because the Russian had difficulty understanding Bevan's accent, leading to a misunderstanding. "The party broke up in a none too friendly atmosphere," the report noted. One assumes the canapés were also disappointing.

The file was not closed until 1975 - 15 years after Bevan died. Better late than never, as they say at MI5.