On 6 July 1978, proceedings in the House of Commons were halted when protesters threw manure from the public gallery onto the floor of the chamber below. The incident occurred during a debate over the Labour government’s plans for Scottish devolution.

The disruption happened shortly after 04:00 pm as MPs raised points of order pertaining to the Scotland Bill. Several bags containing horse manure were seen hurled from the strangers’ gallery, landing amongst MPs on the government backbenches.

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Labour MP Tam Dalyell, a staunch opponent of devolution, was on his feet at the time of the protest.

Addressing the House on a point of order, Dalyell raised the issue of devolving “betting and gaming” when the disruptions began.

The official record of the commons, Hansard, records two “interruptions” during the course of Dalyell’s speech.

The Labour MP for West Lothian stated: “Secondly – [interruption] – on the question of betting and gaming, I should like to return to the issue that I raised with my right honourable friend the lord president [interruption]. The issue of betting and gaming seems to be an especially complex subject.”

Dennis Skinner, the Labour MP for Bolsover, only narrowly dodged the faecal projectiles.

The commons speaker, George Thomas, rose to address the incident.

Dalyell, however, found himself unable to resume his seat – as MPs are obliged to when the speaker rises. “The bench has been soiled by some of the offensive matter that has just been thrown from the public gallery”, the Labour MP explained.

The speaker requested that Dalyell “sit a little further along” the bench, noted Skinner’s lucky escape and then moved to suspend the sitting.

Thomas told MPs: “I think that it is in the interests of the House if I suspend the sitting for 15 minutes to enable the mess to be dealt with.”

The House was suspended for 20 minutes while the public galleries, not to mention the commons chamber, were cleared. Dalyell returned to conclude his point of order, which was summarily dismissed by the speaker.

At 05:26 pm, the speaker delivered a brief statement informing MPs that a “man and a woman” had been taken into custody as a result of the protest.

Thomas told the House: “I have to inform the House that a man and a woman were taken into custody by the serjeant at arms in connection with the recent disturbance in the gallery this afternoon. I take a serious view of this, and I have directed that they be given into the custody of the civil police.”

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It later emerged that two protesters, including Yana Mintoff, 26-year-old daughter of the Maltese prime minister, had smuggled in the bags of manure hidden under their clothing.

The manure was hurled in protest at the presence of British troops in Northern Ireland and in support of republican prisoners. Mintoff, then a member of the Socialist Workers Party, and fellow protester John McSherry were arrested and later fined £200.

The incident was addressed at greater length on 10 July in response to a point of order from Ivor Stanbrook, the Conservative MP for Orpington. Stanbrook conceded that while there may have been a “humorous aspect” to the protest, the episode also raised questions about the security of parliamentarians.

Skinner also raised a point of order.

On the issue of security, he drew attention to “the fact there are millions of people who suffer from a lack of security in one form or another… There are people on waiting lists for kidney machines, old people dying of hypothermia in winter.”

The speaker thanked Skinner for his intervention and complimented “how fast he moved last Thursday”.

Notwithstanding the protest on 6 July, the Scotland Act 1978, alongside the Wales Act 1978, were eventually passed with clauses providing for referendums in both nations. In the subsequent plebiscites in March 1979, the Welsh proposal was decisively rejected, and while a narrow majority voted for a Scottish assembly, it failed to meet the threshold of 40% of the electorate – as required by a controversial clause in the legislation.

Some years later, Dalyell recounted the protest in an interview with BBC News.

He told the corporation: “I was standing on my feet waxing eloquent about the details of Scottish education and suddenly all this dung showered down. Being a sort of stiff-upper-lipped cavalryman – what the infantry call a donkey-walloper – I was determined to go on speaking, much to the approval of my colleagues.

“Shortly afterwards I went out of the chamber and said to one of the badge messengers, with whom I was friendly and whom I knew to be a former Corporal Major at Horse Guards, ‘Where on earth did they get that manure?’

“His reply I will remember to my dying day: ‘Not us, sir. Too loose.’ So it certainly didn’t come from the Horse Guards or the Life Guards.

“It was thrown by Miss Mintoff, the daughter of the Maltese prime minister, whom I knew. This was all about Malta rather than Scottish education. I didn’t take it personally.”

Mintoff was a candidate in the 2013 Maltese general election.

Of her protest, she later explained: “That was about human rights. I knew people who were subjected to inhuman and degrading treatment in the prisons in Northern Ireland who wanted a united island free of military forces.

“I was particularly close to a mother who had two sons and one husband in prison. I won’t go through their conditions because they were horrendous.”