Identity Cards Bill

At some stage, would the noble Baroness be able to give the basis on which one reaches a figure on, for example, a reduction in the cost of crime? How does one reach such a figure in working out a cost/benefit analysis or in immigration control? We have just been told that the card will not be used for stop and search. Probably everyone in this Committee would concede the importance of strengthening the passport. But surely the only way in which the ID card could be useful for immigration purposes is if you were able to stop someone and insist they produce a card. If they were unable to do so, you would then have a power to arrest. I would like to know how those figures will be reached in order for us to asses whether this is a benefit to which we can put a financial figure.