But Mr Blunkett has sought to reassure critics, saying there will be a six month consultation period.

Here are the key proposals under discussion at a glance:

• There could be a nationwide registration scheme for every British citizen to own a card but no requirement to carry it

• Or a voluntary scheme which people could opt-into

• Computerised cards could store a photograph, finger prints and personal information including name and address

• It could bring together passport and driving licence cards

• Discussions on introducing a unique personal number associated with each holder, either new or an existing number such as the National Insurance Number

• The scheme could be targeted at particular groups, rather than the population as a whole.

• An investigation of how a scheme might be enacted in legislation

• ID cards could be used to clamp down on fraud by checking rights to receive NHS treatment, education and state benefits

• The government calls the ID cards entitlement cards

• Conservatives estimate the cost may reach £700m