Adopting the Alternative Vote (AV) for Westminster elections is likely to lead to more spoilt ballot papers and lower turnout, campaigners against reform claimed today.
No to AV published research highlighting the "damaging" effects of the relative complexity of AV compared with the existing first-past-the-post system.
It suggested that elections in which AV was used had higher rates of accidentally spoilt papers and fewer people taking part.
The campaign has produced a video, to be broadcast on Monday evening, further seeking to demonstrate that AV is confusing.
It depicts students in a classroom struggling to understand how the system works and how votes are counted under the system.
The video is the first of two to be broadcast by each of the campaigns - for and against AV - ahead of the referendum on May 5.
Under AV, which is supported by Deputy Prime Minister Nick Clegg and Labour leader Ed Miliband, votes are cast in order of preference and redistributed until one candidate has at least 50% support.
No to AV said Britain had the lowest level of spoilt ballots in the world under the current first-past-the-post system - less than 1% in last year's general election.
In Australia, where AV is used, 5.6% of ballots were spoilt at the last election, roughly two-thirds unintentionally.
The No campaign also pointed to a decline in turnout in Australian elections after AV was introduced in 1919 - down to 59.4% in 1922 from 78.3% in 1917, the last election under first-past-the-post.
Canada had also seen an increase in spoilt papers in provinces where AV was adopted between the 1920s and 1950s, the research showed.
Matthew Elliott, No to AV campaign director, said: "The Alternative Vote is an unfair, complex and expensive system that could have potentially damaging consequences for democracy in this country.
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"The Yes campaign is trying to claim that AV will improve participation, but as these worrying statistics show, the more likely result is a fall in turnout and an increase in spoiled votes.
"If the aim is to have as many people as possible get involved with our general elections, we should preserve the principle of one person, one vote."
