This year's EU referendum has spawned a plethora of campaign groups for and against Brexit - but in 1975 there was a third camp, the "don't knows".
Farel Bradbury, a design engineer from Ross-on-Wye, founded the small but lively Don't Know Campaign after a conversation with a friend in which they discovered neither of them had read the Treaty of Rome, which paved the way for the European Economic Community (EEC).
He decided to print up a leaflet which asked signatories to confirm they had not read the Treaty of Rome and that they paid taxes to government for these matters to be decided on their behalf.
The campaign was run by Mr Bradbury and six other intrepid volunteers, who printed pamphlets and posters bearing slogans such as "pass the buck back to Westminster - where it belongs".
Their request for official funding like that allocated to the leave and remain campaigns went unanswered - but they were not alone in their assessment of the problem.
'Unpleasant and cowardly'
As the EEC bill passed through Parliament, the Conservative MP Michael Latham led an attempt to amend the EEC bill by proposing there should be squares on the ballot paper for voters to mark either "don't know" or "leave it to Parliament".
Another Conservative, Janet Fookes, summarised the problem: "On the doorsteps many people said to me 'First we listen to one side and it seems convincing, then we listen to the other and that seems equally convincing. In the end we are more confused than we were when we began'."
Labour's Willie Hamilton agreed: "People should have the right to say 'We prefer to leave this issue to the judgment of those whom we elected last October.' That is what we are elected for."
A letter to The Times published in January 1975 from a W. D. Bissett called for a "Don't Know" option, saying: "There is something unpleasant and cowardly about shuffling the responsibility for success on the ordinary citizen."
"The current debate has become highly emotional and no one is sufficiently well-informed to decide rationally how to vote," two academics from City University wrote to The Times shortly before the referendum took place.
The Don't Knows insisted their position was not based on apathy - they advised voters to spoil their ballots or abstain, and later claimed that the 64% turnout to decide meant that they had come a "convincing second" after the Yes vote.
Dr Robert Saunders, a historian at Queen Mary University of London, says that although the group was "pretty small" it managed to "strike a chord with a lot of people who had doubts about holding a referendum in the first place".
"Britain had never had a referendum before, and there were associations with Napoleon, and with Mussolini and Hitler."
In March 1975 Margaret Thatcher tapped into this suspicion that the device was "un-British" when she called referendums "a splendid weapon for demagogues and dictators" (quoting Roy Jenkins, who was in turn quoting Clement Attlee).
But this resistance was not only felt on patriotic grounds.
Lindsay Aqui, a PhD candidate at Queen Mary, points out that in 1975 the Cabinet Office recorded figures showing 75% of people wanted more information on EEC membership.
"Many people were unclear about what was at stake," she says, "and some even thought the referendum was on joining the EEC."
The government set up an Information Unit with a helpline to answer people's questions.
It was inundated with calls ranging from the serious ("is it more expensive to come out or stay in?") to the bizarre ("will we still be able to buy King Edward potatoes if we stay in?").
There are parallels with the current referendum, she argues, in that some voters feel they are not getting the details they need to make an informed choice.
Dr Saunders agrees, but points out there are important differences between then and now.
"For one thing, we are a lot more accustomed to referendums as a process - they've been used on devolution questions, the voting system and Scottish independence.
"Secondly - for all the talk of 'Project Fear', in 1975 the referendum was held against the backdrop of inflation and the three-day week, and there was a sense that if we made the 'wrong' decision the sky really would fall in."
He adds that despite the decline of trust in public officials since the 1970s, "there is a lot of information out there on the current referendum - fact-checking websites, blogs and short films".
On that note, he says he wouldn't advocate a revival of the Don't Know Campaign.
"As voters, we can take matters into our own hands. 'Don't know' can become 'should find out'."