Ministers were last night steeling themselves for a tough battle over the Government's plans for identity cards (ID) as the legislation providing for a national scheme heads towards a vital Commons vote.

An academic team's report, which is published today, will give critics of the scheme more ammunition - putting a price tag of up to £18bn on the scheme.

Tomorrow, MPs will get their first chance to vote on the proposals since the election, when the Identity Card Bill gets its second reading in the Commons.

Labour backbenchers look unlikely to rebel in sufficient numbers to defeat the Government, but peers seem certain to table a raft of amendments, which could radically alter the scheme when the Bill reaches the Lords.

The Government's most immediate concern yesterday was to rebut a suggestion that the Government could sell personal details stored on the supporting database to help meet the huge costs.

In a statement, Immigration Minister Tony McNulty said: "The suggestion that the Government intends to 'sell' information on the ID cards register is complete and utter nonsense.

"The legislation we have introduced to set up the scheme will ensure that the ID cards database will be secure and confidential."

But he acknowledged that banks and other organisations would be accredited as database users and able to refer to it for identification verification purposes.

Earlier, Labour backbencher Bob Marshall- Andrews predicted that between 20 and 30 colleagues could sign up to a rebel amendment.

Nineteen Labour MPs rebelled over the issue in the last Parliament, and the Tories and Liberal Democrats have said they will vote against it.

Today, the London School of Economics (LSE) will publish a detailed report on the scheme's feasibility.

In March, the LSE's draft report estimated the project could cost between £12bn and £18bn over ten years.

Basing their calculations on those figures, some commentators estimated that each card could cost £300.

Home Secretary Charles Clarke dismissed that as "a complete nonsense figure".

While emphasising that its report had not suggested an individual card figure, the project team stood by its estimate for the overall cost.