Westcountry councils have been accused of breaching the privacy of hundreds of thousands of residents by selling their names and addresses.
The authorities sold the information on the edited electoral role to dozens of companies, charities and individuals.
Privacy campaigner Big Brother Watch (BBW), which compiled the study from Freedom of Information requests, called for a change in the law.
But local authorities said their hands were tied – and said anyone can have their name removed from the edited version of the electoral register, which is available for sale.
Cornwall Council cabinet member Alex Folkes, portfolio holder for finance and resources, said: "It is unfair to blame the council for sales of the register and any subsequent junk mail people may receive when the council is just following the law," he said.
According to BBW, Cornwall Council sold versions of the edited electoral role six times, including to Ocean Housing, Coast, and Estuary Cottages, making a total of £154 from the deals.
Mr Folkes said the authority had followed the law by producing two versions of the electoral register – one used on polling day and an edited version which may be sold to organisations or individuals.
He said anyone on the roll could opt out of the edited version by simply ticking a box.
Authorities were unable to alter the forms, and providing further information advising people of this would be a costly endeavour for the council, he said, adding: "I would rather pay for adult care."
According to BBW, 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 organisations as varied as estate agents, lobbyists and solicitors, among others.
Plymouth City Council sold the edited roll six times, including to J Thorpe Furniture and Plymstock Parish Church for a total of £407.
A spokesman for the authority said: "All councils need to follow the statutes and regulations relating to electoral registration.
"The Electoral Commission website sets out the legal position and clearly indicates that there are two versions of the electoral register and that the edited version has to be available for general sale and can be used for commercial activities such as marketing. We provide an 'opt out' box on our registration form for residents who wish their name to be kept off the edited version of the electoral reg-ister."
West Devon District Council sold the roll eight times, including to Okehampton East Residents Association and communications consultancy JBP Associates Ltd, , making a total of £278.
A spokesman for West Devon District Council said the report produced by BBW would be scrutinised. "We will be noting the report and looking at the figures," he said.
According to BBW:
Exeter City Council made six sales of the edited register for a total of £647.
The Isles of Scilly Council sold the register once to an individual for an undisclosed sum.
Mid Devon District Council was paid £570 for sales to "unspecified" customers.
South Hams District Council sold the edited register 19 times, to 15 individuals and others including Dartington Hall. The sum paid was not detailed.
Teignbridge Council was paid £258 for an unspecified number of sales.
Torridge sold the roll twice to a marketing company and solicitors firm for £142.
Devon County Council, and district councils covering East and North Devon and Torbay, all said they were not responsible for electoral roll data or did not hold the information.
BBW 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 that 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."