Nick Clegg has insisted there are no Liberal Democrat fingerprints on the notorious 'go home' vans aimed at illegal immigrants.
Clegg also distanced David Cameron from the campaign, branded #racistvan by critics on Twitter, and said it was not a "clever way of dealing with this issue".
Yesterday Downing Street insisted the vans, which were piloted in London last week, were working and said they had been signed of by the 'Home Office team', taken to include Lib Dem minister Jeremy Browne.
But on Tuesday, Clegg told BBC Radio 5 Live: "It's not something which requires the permission of the Prime Minister or the Deputy Prime Minister, and didn't require or receive the consent of the Liberal Democrat in the Home Office."
Tory immigration minister Mark Harper used a Daily Mail article to defend the no-nonsense approach, criticising the "astonishing" reaction from what he called the "pro-immigration industry".
Clegg, however, challenged Harper over the pilot scheme, which saw the vehicles travelling around parts of London, and urged him to focus on introducing proper entry and exit checks at the borders.
He was "very surprised" by the pilot scheme and added: "I think people should play by the rules and play by the law. I want to see us make sure that the public have confidence in the immigration system, that it works properly.
"I don't happen to think that having a couple of vans driving around north London is the way of actually inspiring public confidence that we have an immigration system that is working properly."
He added: "I said to the Home Office in very clear terms, I was talking to the Immigration Minister yesterday - he's a very good guy, by the way, Mark Harper - I was saying the effort that should be spent is not on vans drifting around North London but on actually reinstating exit checks which I think were wrongly removed in the past and which we are committed to, and this was on my personal insistence, committed to reinstating as part of our coalition agreement."
On Sunday, Lib Dem Business Secretary Vince Cable described the van-based campaign as "stupid and offensive" but was slapped down by No 10 over his comments, with the Prime Minister's spokesman claiming it was already "working".
A Home Office spokesman said the impact of the vans, which finished their advertising patrols on Sunday, was yet to be fully assessed as a poster and leaflet campaign was due to continue for another three weeks.
Clegg said: "Unless there is overwhelming evidence that this is a really effective way of bolstering public confidence in the immigration system and bearing down on illegal behaviour in the immigration system, I'm going to need a lot of persuasion.
"What are we going to have next? Home Office vans driving around saying 'please don't shoplift' or 'please don't steal this car'?"