http://www.publications.parliament.uk/pa/cm200910/cmselect/cmhaff/170/170.pdf

… where the committee says:

48. We conclude that it is only in exceptional cases, based exclusively on the conduct of the individual concerned rather than as part of a blanket requirement, that an EU Member State can impose any requirement other than simple production of a valid identity document to restrict the entry into or exit from that Member State of an EU citizen. The e-Borders programme is therefore, as far as we can ascertain, likely to be illegal under the EU Treaty.