Tories admit scheme was 'blunt instrument' which only one person took up – after reading about it in the Guardian

Theresa May yesterday admitted that the Home Office's controversial "go home" vans had been "too much of a blunt instrument", as she confirmed they would not be extended nationwide.

The Home Office came under fire for using the ads, displayed on billboards carried by vans in six London boroughs, reading, "In the UK illegally? Go home or face arrest."

In comments to MPs, May said she had studied an evaluation of the campaign and concluded it should not be taken further. "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."

The full evaluation will be published shortly but it is believed that only one illegal immigrant agreed to go home – and that was a result of reading about the vans in the Guardian.

She said the experiment trialled in parts of London in July was not going to be extended during the second reading of the immigration bill.

The decision is a blow to Mark Harper, the immigration minister, who said last week on BBC1's Question Time the venture might be extended. May had always been more reluctant to embrace the idea, including when before the home affairs select committee last week.

The decision led to another row between the Liberal Democrats and the Conservatives on responsibility for the decision to scrap the scheme.

The Lib Dem president, Tim Farron, tweeted "we did it", as other party sources claimed that Norman Baker, the new Home Office minister, had pressed for the trials not to be extended.

Farron said: "It is right that this pilot scheme is scrapped and that these vans will not been seen on our streets again. The vans represented the worst kind of divisive politics and it seems only one immigrant went home because of them. This is a failed project and the Home Office should hold their hands up and admit it was wrong both practically and morally.

"It is important that our borders are protected and secure but this policy – driving a van around some of the most diverse communities in London – is not the way to deliver that."

Liberal Democrats said that they opposed the vans as a matter of principle. But Conservative sources said the decision had been taken by May after the evaluation showed the vans had not been effective in persuading illegal immigrants to leave the country.

The business secretary, Vince Cable, had described the vans as stupid.

Julian Huppert, a Liberal Democrat home affairs committee member, said the vans had demonised people who were in the country legitimately.

Gavin Barwell, the Conservative MP for Croydon, praised May's announcement, saying it was "the right decision not to continue ad vans aimed at illegal migrants", adding there were much better ways of tackling illegal migration.

Shadow home secretary Yvette Cooper branded the vans a divisive gimmick. The project was a complete failure that was beneath May and "ought to be beneath this government".

Cooper insisted that Labour's plans on immigration, which include trebling the maximum fine for employing illegal workers to �£30,000, were a contrast to the government's "gimmicks" such as text messages and "offensive" advertising vans.

"The government is failing to address the exploitation of low-skilled immigration in the labour market. Nor do they have any serious strategy for tackling illegal immigration.

"That's why we are setting out sensible and practical policies, instead of the Tory-led Government approach of resorting to ineffective and offensive ad vans, gimmicks or incorrect text messages to people who have lived here for 30 years."