More than 300 local authorities sold people's names and addresses to more than 2,700 companies and individuals over a five year period.
According to Freedom of Information Act requests made by Big Brother Watch, councils sold the edited electoral register - made of up all those people who register to vote and do not opt-out of the edited version – to places such as pizza shops, estate agents, lobbyists and driving schools.
Some 307 local authorities sold the edited electoral register to at least 2,742 different companies and individuals between 2007 and 2012, raking in at least £265,161.21 for local authorities.
The council with the most buyers was Westminster, which sold it 93 times, while three other councils - Elmbridge, Kensington and Chelsea and Broadland - sold the edited register to more than 50 buyers.
Big Brother Watch has called on the Government to abolish the edited register but if it is to be retained, the group are urging the Cabinet Office to allow councils to include a permanent opt-out option on the electoral registration form, something currently not possible due to statutory provisions.
Big Brother Watch director Nick Pickles said: "Registering to vote is a basic part of our democracy and should not be a back door for our names and addresses to be sold to anyone and everyone.
"Many people don't realise the pizza shops and estate agents drowning their doorsteps with junk mail are able to do so because their local council is forced to sell the names of every voter who fails to tick the right box when they register to vote.
"The edited register is a pointless waste of council time, undermines trust in the electoral system and contributes to huge volumes of junk mail. It should be abolished."
A spokesman for the Department for Communities and Local Government said: "It is completely unacceptable for councils to be profiting in this way.
"Junk mail is a menace and councils should be looking at ways to make sensible savings and not taking advantage of voters."