It’s not common, but there is a history of banned songs at Eurovision. Sometimes one country will boycott another's entry and refuse to play the portion of the broadcast containing the offending tune, such as Jordan’s decision in 1978 to screen images of flowers rather than admit Israel had won.

In 2005, Lebanon’s debut in the contest was indefinitely postponed over their refusal to show the entry from Israel. And in a rare non-Israeli example, Georgia’s “We Don’t Wanna Put In” was removed from the 2009 contest after Russia finally got the joke.

But only Gigliola Cinquetti managed to have her country’s song banned… by her own country. In 1974, Cinquetti was returning triumphantly to the Eurovision stage. Ten years earlier, at the age of 16, she had won the contest for Italy with the not-at-all-dodgy "Non ho l'età" ("I'm Not Old Enough").

Her latest song, “Si”, was considered a favourite to win. But Italy would not get to see Cinquetti emoting her heart out while wearing a frock that looked like several blue lampshades stacked haphazardly and apparently being backed by the Kranksy Sisters.

Looking at the footage now, it’s hard to see why the song was banned. “Si” tells of a woman who – according to a surprisingly wistful Wikipedia entry – “reflects and describes her love for a man, and the exhilaration she feels when she finally says 'yes' to him”.

“Sì, dolcemente dissi sì/Per provare un’emozione/Che non ho avuto mai,” Cinquetti sings. “Yes, I softly said yes/To feel an emotion/That I never had." It certainly wasn't the 1970s equivalent of "Smack My Bitch Up".

The reason the ban seems confusing now is because the reason lies not in the song, but in the country itself. In 1974, Italy was facing a referendum – the first for the country – on the issue of divorce. Divorce had only been legal for four years and many church groups were appalled this largely Catholic country had allowed such a thing. They had successfully agitated for a referendum on the new law, hoping to return Italy to the good old days when marriage was forever (except in the case of murder and/or adultery).

There was belief that Cinquetti’s repetition of the word “si” – or “yes” – 16 times during the song might sway the voting public, especially if it became a hit. Yes, the Italian Eurovision entry of 1974 was banned for fear it would subliminally effect the outcome of a referendum on divorce. It's like a disco-era retelling of The Manchurian Candidate.

To complicate matters further, because the referendum wasn’t about whether divorce should be legal but whether divorce laws should be struck down, there was confusion around what saying “si” actually meant. To keep divorce, you had to vote no, because you were objecting to the removal of the law that said yes to divorce. If you wanted divorce struck from the books, you had to say yes, which meant no divorce.

In the end, “Si” came second at Eurovision, beaten by some one-hit Swedish act called ABBA. Italians voted to keep divorce, 60 percent to 40 percent, although there is belief the pro-divorce vote was actually higher if you factor in people who didn’t understand the question.

Cinquetti’s song went on to be a hit in several countries, just not the one she came from. Often rerecorded for the local market, in France, it became “Lui” and in Germany “Ja”. It even cracked the UK top 10 with the totally new title, “Go (Before You Break My Heart)”. Forty-two years later, the UK would have a referendum on the European Union, which would be won by the “leave” campaign. Coincidence?

The Eurovision Song Contest will be broadcast over SBS’s Eurovision weekend - Friday 12 May, Saturday 13 May, and Grand Final Sunday 14 May at 7.30pm on SBS with LIVE early morning broadcasts begin Wednesday 10 May at 5am on SBS.