More people are seeking to keep their names and addresses off the electoral roll.
Official figures show the number of people listed on the unpublished electoral roll has doubled in eight years - from 7600 in 2004 to 15,500.
The roll enables people to register to vote without their names and addresses being publicly accessible.
The Electoral Commission credits a publicity campaign telling victims of family violence they can register to vote without their address being published.
But it says it does not record the categories of people who apply.
