The revelation, in an obscure Whitehall consultation paper, calls into serious doubt the Government's repeated promises that planned ID cards, already hugely controversial, will be voluntary and that no one will be forced to carry one.

Those who fail to register for an ID card could be fined up to £2,500

It will stiffen resolve at Westminster to oppose the Identity Cards Bill, which is due before the Lords again next week.

Peers are already vowing to water down the plans to ensure that registration for cards is voluntary. At present the Bill requires people to submit their details to a new national ID Card Database when they apply for a passport, in effect making registration compulsory.

The small print of a consultation paper published by Lord Falconer's Department for Constitutional Affairs, released during the Christmas holiday, reveals that town hall officials will be asked to police the scheme by using the Electoral Register to identify homes and individuals without cards.

The register will be cross-checked against the proposed Identity Card Database in what the Conservatives are calling "Big Brother" tactics. Those who fail to register for a card or to keep their details up to date when, for example, they change address face fines of up to £2,500.

In baffling language, the document proposes a shadowy sounding system called "Core" - and discusses the need for "data sharing" and "unique, personal identifiers". (Core is a new centralised, electronic electoral register to replace the current, locally managed registers.)

It suggests that electoral registration offices (EROs), at local councils could help to provide information for the proposed ID Card Agency by scouring their systems.

"With a Core consolidated dataset, it should be possible to check elector records against a dataset requiring much higher levels of verification. The other dataset might also make notification of changes to personal details or addresses a requirement and discrepancies could be referred back to an ERO for investigation.

"The anticipated high level of security checking and intended requirement for citizens to notify changes may make the ID card register dataset a particularly useful comparator."

The plans for heavy policing of the scheme fly in the face of promises by Tony Blair that the cards would be voluntary, a promise repeated in Labour's manifesto for the general election in May last year. Charles Clarke, the Home Secretary, promised three months ago that ID cards "will not create Orwell's Big Brother state".

Last night Oliver Heald, the shadow constitutional affairs secretary, said: "There is growing concern among the public about Labour's use of invasive 'Big Brother' computer databases - without transparency or clear backing from the public - such as for the forthcoming council tax revaluation.

"I believe local residents will be alarmed at the further prospect of town hall bureaucrats being told to investigate people's homes for ID cards, backed up with the threat of thousand-pound fines."