Not unlike the US, the UK has contentious politics regarding immigration in general and illegal immigration in particular. This has come to the forefront in the hubbub over a pilot program by the coalition government to remind illegal immigrants that they should self-deport:
I'm trying to imagine the reaction if the same thing was tried in certain neighborhoods in DC and northern Virginia.
Anyway, Labour and Liberal Democratic politicians were quick to rubbish this scheme, since it looks remarkably like a rolling billboard version of the "go home" grafitti back in the day, as well as being kind of dumb. The government responded that all they need for a positive return on investment is for one illegal immigrant to bugger off home, as it cost the government £10k to get the poster, and costs them £15k for each involuntary deportation.
The real sign that this is a bad idea, though, is that the leader of the anti-immigration / anti-EU UK Independence Pary has described the signs as unpleasant and pointless, and accused the Tories of pandering for votes lost to UKIP.
All in all, I'd say that's a pretty good sign (if you'll excuse the choice of phrase) that the UK government got it wrong.
Let the slapfights begin!