Why not just save the money to be spent under the bed, let anyone who wants to come in and stay regardless.
Why do I say that? Because I have no faith HMG will be able to deliver this (or any other IT project) on time, on budget, and actually fit for purpose. They can't do it with passports, a supposedly secure document, The ID card project (regardles if uou agree with it or not) already has cost issues, when they do supposidly run checks they are often miss the obvious and grand approval to people they shouldn't anyway and then when they are found to be illegally here they can't manage to deport them back to the country of origin.
It seems a good idea but someone in HMG will seize on it and change the scope halfway through and just make a complete pigs ear of it. And if they don't they'll probably lose the disk with the data on the day before they need to use it anyway.