The Advertising Standards Authority (ASA) said it had received 60 complaints about the mobile billboards including concerns the ads were “reminiscent of slogans used by racist groups to attack immigrants in the past”.
The ASA probe is in addition to another investigation by the Equality and Human Rights Commission (EHRC) into a wave of immigration spot checks across the country.
Chris Bryant MP, Labour’s shadow immigration Minister, said: “This is another embarrassing blow to a Government which continues to fail to deal with immigration.
“With more people absconding at the border and fewer illegal immigrants being returned, David Cameron and [Home Secretary]Theresa May can’t even get the basics right, stumbling from one shambles to another.
“You’ve got to question the Government’s competence.
“We need effective action on immigration not offensive stunts.”
Ads warning overstaying migrants to “Go home, or you’ll be picked up and deported” appeared last month in six London boroughs.
Migrants’ rights groups, Labour politicians and unions reacted to the campaign with anger and disgust.
The ASA said some complainants have also questioned whether a claim in the advert reading “106 arrests last week in your area” was misleading.
An ASA spokesman said: “I can confirm that the Advertising Standards Authority has launched a formal investigation into the Home Office ‘Go Home’ ad campaign following 60 complaints.
“Complainants have expressed concerns that the ad, in particular the phrase ‘Go Home’, is offensive and irresponsible because it is reminiscent of slogans used by racist groups to attack immigrants in the past and could incite or exacerbate racial hatred and tensions in multicultural communities.
“Separately, some complainants have challenged whether the claim ‘106 arrests last week in your area’ is misleading.
“They’ve also challenged whether it is misleading because it implies arrest is the automatic consequence of remaining in the UK without permission.
“We will publish our findings in due course.”
A spokesman for the Home Office said: “We can confirm we are in contact with the ASA over this investigation and we will respond in due course.”
Crossbench peer Lord Ouseley, former chief executive of the Commission for Racial Equality, told BBC Radio 4’s The World At One the advert added to a climate of “racism and xenophobia”, while Tory backbencher Peter Bone MP said the pilot should be rolled out nationwide if it is effective.
The EHRC launched its probe after it was claimed that the spot checks – conducted at transport hubs up and down the country – were being carried out by border officials purely on the basis of ethnicity.
Rachel Robinson is policy officer at human rights campaigners Liberty, which launched its own vans with the alternative slogan ‘Stirring up tension and division in the UK illegally? Home Office, think again’.
She said: “Another day, another sign that this cheap Home Office stunt has seriously backfired. Driving National Front-style slogans around ethnically-diverse areas was bound to cause deep offence.
“The Home Office have a duty to promote good relations and eliminate discrimination – it’s time for them to think again.”