James Purnell (Secretary of State for Work and Pensions), is talking about bringing lie-detectors in to help find people who are lying in order to get benefits.
Problem is that lie detectors don’t work (last item). They tend to give many false positives, which means more work for people to do to investigate claimants (and despite the idea that the benefits agency won’t take a failed test as evidence, the suspicion will likely be there for some time) but they can also be beaten by people who look up a few ways to do it. More info here.
EDIT 5 Dec 15:33 – I saw a very interesting (and far more detailed) analysis from Unity today. Essentially he’s saying that lie detectors can ‘work’, but for detecting stress, rather than for detecting lies (honest people can be stressed under questioning, and liars can be ice-cold)