Councils will gain powers to cross-match their databases in an attempt to increase the number of people on the electoral register, said deputy prime minister Nick Clegg.

Clegg said there was "no excuse for inaction" in response to estimates that 3.5 million valid voters were not on the electoral roll, according to a BBC report.

Database matching pilots next year, said Clegg, will enable councils to identify the people who are missing, so council officers "will be able to help these people onto the register".

However, there are concerns among privacy campaigners that such a move may in fact endanger data security. NO2ID, which successfully campaigned against the introduction of national ID cards, warned against the database matching scheme.

NO2ID national coordinator Phil Booth said, "On the one hand the government have said they want to roll back the database state, but now they seem to be saying we are going to use this data just because we have it.

"It breaks the first principle of data protection, which is that you don't use data gathered for one purpose for another purpose."

If the pilots are successful, Clegg said database matching would be rolled out across the country.

Any new powers would be studied closely, to see whether they could be used for other means. The Information Commissioner recently criticised councils for using CCTV powers designed to tackle crime, to instead track citizens for alleged minor misdemeanors, such as registering their children at schools that were not in their catchment area.