LONDON (AFP) - Britain said on Tuesday it would not extend a much-criticised campaign of vans displaying posters urging illegal immigrants to go home or face arrest, admitting it was "too much of a blunt instrument".

In a pilot campaign in July, posters displaying the message "In the UK illegally? Go home or face arrest", were driven around areas of London on the back of several vehicles.

They were part of a wider clampdown on immigration by Prime Minister David Cameron's Conservative-led coalition government, but they were condemned for being offensive and ineffective.

Home Secretary Theresa May, the head of the interior ministry, told lawmakers in the House of Commons that an interim evaluation of the pilot had shown "some returns".

But she said: "Politicians should be willing to step up to the plate and say when they think something actually hasn't been as good an idea, and I think they were too blunt an instrument."

Business Secretary Vince Cable, a member of the Liberal Democrats who are the junior partner in the coalition, had described the campaign as "stupid".

The opposition Labour party accused the government of employing language used by far-right groups in the 1970s.

Britain's advertising watchdog received hundreds of complaints about the posters.

It said the posters should not appear again in their current form because they used misleading statistics, but ruled that they were not offensive.

Britain also sent text messages to almost 40,000 illegal immigrants warning them they had no right to remain, but the scheme backfired when a few of the messages were sent to the wrong recipients, including one British anti-racism campaigner.