Officials are being allowed to trawl databases including the Royal Mail and the Student Loans Company to track down missing voters in a new trial.

Data matching could be used to fill in gaps in the electoral register ahead of the launch of individual voter registration in 2014.

Ministers say the technique is as accurate as ID cards - but it has raised privacy concerns.

Labour peers said it would have been easier if ID cards had been introduced.

The ID card scheme was scrapped by the coalition government on privacy, cost and civil liberties grounds - but the Electoral Commission is now faced with the problem of verifying the identity of millions of voters without a central register.

'Astonishingly cheaper'
Labour peer Baroness Hayter said the government "is no doubt ruing the day" it decided to scrap ID cards.

"All these hurdles they are now trying to go through to get a more accurate electoral register would not have been there if we had kept ID cards," she told BBC News.

In a debate last week in the House of Lords, Lord Maxton said: "None of this would have been necessary - I will not mention ID cards because for some reason they are not considered politically correct - if we had smart card technology with a central database."

But Lib Dem minister Lord Wallace of Saltaire said it was possible to verify people's identities using information held on different government databases.

He told peers: "We do not rue the day when ID cards were dropped, but we are persuaded that developments in the computer and electronics world, and the way in which it is possible to use digital databases and compare among them, is opening up the possibility of providing identity assurance and a simpler relationship between the citizen and the state, which would not only be more efficient but astonishingly cheaper than the original ID scheme."

Under the government's voter registration plan, each member of a household would have to register individually.

At the moment, one householder supplies details of other people living at the address.

The aim is to cut down on electoral fraud - but it depends on being able to track down individuals who have never been on the electoral register or who have moved house and dropped off the system.

An Electoral Commission investigation in Northern Ireland, where voter registration has been in use since 2004, found there had been a "serious decline" in the accuracy of the electoral register because officials have been unable to keep pace with people changing addresses