The figures are based on the data that Skipton has collected so far from more than half the councils in the UK.
The increase means that an average of 28.5% of the roll is opted out, compared with 26% a year ago and 20% two years ago. But rates vary widely by geography, from as low as 4.5% for Powys in Montgomeryshire to as high as 72.3% for Wandsworth.
Mike Green, CEO of Skipton, which owns CallCredit and EuroDirect, said: "We are starting to see a disconcerting trend in data loss, which shows that the marketing industry still needs to be aware of the importance of supplementing the Electoral Roll with other data sources to maintain access to the consumer universe."
Green pointed out that marketers using the Electoral Roll as their primary source would find it almost 30% less effective than the full version, and significantly less effective in specific regions.
Local councils, including Wandsworth, have been criticised by the DMA for pre-ticking opt-out boxes on fresh forms sent to people who opted out last time, especially for the current Roll.
However, the Association of Electoral Administrators brought in regulations after this year's forms were printed, which are likely to prevent councils from pre-ticking opt-out boxes in next year's forms.
A spokesperson for Experian said: "We know from 2003 that predicting opt-out rates is difficult due to the pre-ticking of boxes."
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