Initial findings from Experian and Equifax show that the opt-out rate in the 2003 Electoral Roll returns increased by more than a third from 20 per cent to 27 per cent, a rise of 2.4 million electors.
The rise is largely being attributed to the prefilling of forms. Almost 400 councils submit details of electors in the annual canvas, and about 60 per cent of these prefilled last year's forms, making it easier for people to re-opt out.
Opt-out rates range widely between councils, with Bridgend having the highest opt-out rate at 84 per cent, compared with Lanarkshire, which has the lowest at only three per cent. Some councils also experienced a fall in opt-out.
The reason for these differences is as yet unclear, according to Patrice Bendon, senior product manager at Experian.
"The trend is for higher opt-out rates, but we can't see a pattern," she said. "The main reason is prefilling, but it could also be down to how data was collected, with some councils conducting a door-to-door canvas."