The prime minister threw his weight behind the idea publicly for the first time when he addressed delegates last Tuesday.
Blair said, "In a world of mass migration, with cheaper air travel and all the problems of fraud, it makes sense to ask whether now, in the early 21st century identity, ID cards are no longer an affront to civil liberties but may be the way of protecting them.''
The home secretary wants the cards, which would carry biometric data and a digital signature, to help in the fight against illegal immigration, benefit fraud, identity theft and organised crime.
But trade secretary Patricia Hewitt has questioned the strategy, saying ID cards raised "enormous questions'' of principle and practicality. "Great big IT projects, databases and the rest of it have a horrible habit of going wrong,'' she said on the BBC's Question Time last week.