Next week sees a rare public hearing of the Undercover Policing Inquiry (UCPI), which was launched in 2015 following the ‘spycops’ scandal to investigate undercover police operations over five decades.

Starting on 20 February, the inquiry will sit virtually for three days to hear closing statements for ‘Tranche 1’, which covers the period from 1968 to 1982. These will summarise the evidence heard on undercover policing during this time and how governments worked to cover it up.

By now, most people will have read something about the women deceived into relationships by undercover officers or police spying on the family of Stephen Lawrence or other Black justice campaigners.

But the inquiry, whether by choice or ignorance, is not paying as much attention to the police’s spying on trade unions – a hidden but important element of undercover state surveillance.

Two secret policing units – the Metropolitan Police’s Special Demonstration Squad (SDS), part of the force’s Special Branch, and the National Public Order Intelligence Unit (NPOIU) – spied on supposed ‘subversives’ within British society, including protest groups and left-wing activists. The spying started with the Vietnam Solidarity Campaign in 1968 and continued into the first decade of this century, when climate activists were the targets.

Industrial disputes were of key interest to the SDS from the start. Miners, dockers and construction workers were all spied on during strikes in 1972, according to the SDS’s annual reports.

But the police were not merely attending public picket lines and protests. Undercover police officers with false identities were joining unions. SDS officers using the cover names ‘David Hughes’ and ‘Barry Tompkins’ joined the Transport & General Workers Union in the 1970s and early 1980s, the inquiry has confirmed.

Another undercover officer, Mark Jenner (cover name ‘Mark Cassidy’), infiltrated the construction union, UCATT. From 1995 until 2000, when he ‘disappeared’, Jenner regularly attended meetings of the Hackney branch, participated in the union’s decision-making processes and played a leading role in a safety campaign for workers. He also deceived ‘Alison’, a teacher and union member, into a five-year relationship during his undercover deployment.

Missed opportunities or refusal to investigate

There have always been rumours about ‘Special Branch’ units spying on trade unions, but the British state had never seen a reason to launch an investigation into such practices – until it was forced to in the wake of the spycops scandal.

Even now, the UCPI seems intent on missing crucial opportunities to answer the question of why SDS surveillance was allowed to continue for so long.

Take the famous Grunwick strike, a two-year-long dispute beginning in 1976 at the Grunwick film processing labs in north London. We know from the UCPI’s previous public hearings last year that at least seven undercover officers, three of whom have been granted anonymity by the inquiry, attended the Grunwick pickets. Special Branch sent officers as ‘spotters’ to gather the names of people who took part, and the SDS infiltrated left-wing political groups that joined the picket lines.

In 1977, the Daily Express ran a front page with the headline ‘The Secret Demo Squad, Special Branch men to join pickets’, writing: “The undercover men already have thick dossiers on extremists. The authorities are anxious to establish whether there are links with political organisations whose aim is solely to disrupt industry.”

Unfortunately, this clipping is not among the files disclosed by UCPI, which decided not to investigate Grunwick in any detail.

Although the dispute featured as a major public order event in the SDS’s 1977 annual report, the UCPI disclosed only six reports about the strike (the Grunwick strikers chose not to participate in the inquiry, so it is not required to release more).

It’s a missed chance for the UCPI, which is investigating only those events and issues for which ‘core participants’ to the inquiry were spied on. It’s also unnecessary, as plenty of material on Grunwick is already in the public domain, including documents in the National Archives and formerly secret files released through Freedom of Information requests that would have allowed the UCPI to analyse Special Branch’s threat assessments.

The National Archives files show that reports about Grunwick, based on intelligence gathered by undercover police officers, went all the way up to the home secretary of the day and sometimes even the prime minister.

In a 1974 meeting with home secretary Roy Jenkins, Labour MPs including John Prescott raised the issue of Special Branch spying on unions. They asked for an inquiry into infiltration and the exchange of information about potential troublemakers between police and employers.

Documents disclosed by UCPI show Jenkins denied the police spying, telling the MPs: “There was no question of Special Branch infiltration into trade unions directly or indirectly”. Prescott countered that “he felt sure there was such infiltration”. He was right.

After a follow-up meeting between Jenkins and MI5 head Michael Hanley, Home Office civil servant James Waddell summarised the actions needed to address the concerns. He strongly advised the prime minister, Edward Heath, that “we ought not to be too sweeping in anything said about infiltration”, explaining that Special Branch (in addition to MI5) did indeed infiltrate subversive bodies and that “denials about their interest in the unions may be disbelieved”.

Instead of addressing the MPs’ fears, Waddell advised the home secretary to try and avoid further leaks. He said: “In view of the sensitivity of the subject, it would be as well to remind Special Branch officers about the particular need for care and discretion in the industrial field.”

The Security Service would indeed send a circular letter to all Chief Constables in the UK in late May that year. It included a warning not to share information with anyone outside the police.

As deputy under-secretary at the Home Office, Waddell was responsible for the police, public order and security; he was involved in setting up the SDS and signing off the unit’s annual funding until his retirement in 1975. He also chaired several secret Cabinet committees that worked to counter “subversion in public life”.

Blacklisting practices

While the official policy quoted to MPs and the media was that covert intelligence was never shared with employers, Home Office practice was often completely the opposite.

National Archives documents show that in 1973, when the chairman of tractor maker Massey-Ferguson asked a senior civil servant at the Home Office for details about possible troublemakers at his Midlands plant, both the head of MI5 and senior civil servants initially opposed the idea.

Waddell advised that “the general policy of not giving information from official sources… is well-established”, adding that “ministers have generally accepted that the most we should do is refer the enquiring industrialists to unofficial sources like the Economic League.”

He added: “I think the feeling has been that anything in the way of an official blacklist might both hamper [redacted] and put the government of the day at risk of attack for interfering in the employment field.”

But after a fortnight of lobbying, the prime minister himself, Edward Heath, interfered, saying: “Mr Powell of Massey-Ferguson is too serious a person to be dismissed with a reference to the Economic League.” He added: “There is a case for being prepared to give some degree of oral briefing in trustworthy cases”. A meeting between the industrialist and the Home Office was duly arranged.

This correspondence shows how easy it was to get a private briefing on subversive organisations, if you had the right contacts, and confirms the cooperation between the Cabinet and the Economic League, a notorious blacklisting organisation that created a list of alleged left-wing workers, which its corporate members could use to vet job applicants. The Economic League, which was founded in 1919, eventually closed in 1993 following media investigations and a parliamentary inquiry.

But the UCPI has chosen not to include this file in its evidence bundle.

The SDS’s infiltration of trade unions and the sharing of intelligence with employers are both fundamentally undemocratic. The involvement of the Home Office and various prime ministers over many years reflects the political oversight – or lack thereof – of such activities. Investigating these blacklisting practices is pivotal to understanding the nature and workings of the secret state.

The UCPI still has plenty of opportunity to scrutinise the surveillance of the labour movement as it is expected to run until 2026. But its failure to disclose critical evidence, or even to examine the wealth of documents already publicly available at the National Archives, casts serious doubt as to whether the inquiry has any real intention of exposing the full extent of political policing in the UK.