The Electoral Commission has called on the government to think again on proposals which would allow direct marketing firms to buy copies of the electoral register.

The intervention comes after ministers put forward proposals which would allow the full register to be sold to credit reference agencies and the creation of a second "edited" register available for general sale.

The elections watchdog argues it is wrong for personal data, which is collected compulsorily, to be sold on.

The commission has expressed concerns that the commercial exploitation of the voters' roll could hit registration numbers.

Sam Younger, the chairman of the Electoral Commission, said: "We have urged government to re-think its proposals for the sale of electoral registers which we believe to be wrong in principle.

"The registration of voters is an essential part of our democratic process and to exploit the information provided for commercial purposes could well discourage registrations."

The commission has also urged the government to re-think its proposals to provide an edited register.

If the government sticks to its plans for a second register, the commission says it should be compiled on the basis of electors having to positively "opt in" to having their details sold.

Under the government's current proposals electors who do not want their details sold on will have to "opt out" of the second list.