The campaign for the Government's EU Settlement Scheme failed to make it clear to applicants they would need other documents in addition to a passport or ID card to apply, according to a decision by the Advertising Standards Authority (ASA).
The radio advert, heard in April, said: "If you're an EU citizen living in the UK, you will need to apply to the EU Settlement Scheme.
"The scheme is fully open and you have plenty of time to apply.
"It is free and all you need is your passport or ID card and to complete an online form.”
The ASA said it understood applicants in 27% of decided adult cases had been asked to provide additional documents as evidence of residence.
The scheme aims to help EU citizens and their families live and work in the UK after freedom of movement ends.
Applicants must prove their identity, show they live in the UK and declare any criminal convictions.
A complainant who heard the advert said they understood that in come cases applicants also needed to provide proof of address covering the previous five years and challenged whether the ad was misleading.
The Home Office said it ‘completely disagreed’ with the ASA decision, saying at no point was any applicant to the EU Settlement Scheme asked to provide proof of address as part of the application process.
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It added, however, that it was not possible in the format of the advert to "cover all eventualities”.
The Home Office said in 73% of cases applicants did not have to submit any documents as evidence of their residence.
Upholding the complaint, the ASA said the advert referred to the minimum documents required to complete the initial application form and listeners would infer these were all they would need to complete the entire process of applying for EU settled status.
It said: "Listeners would likely understand that an official application process of this nature would always require some applicants to provide further information in exceptional cases.
"However, we understood that in 27% of decided adult cases, applicants had been asked to provide additional documents as evidence of residence.
"Furthermore, some applicants were also asked for other documents, such as evidence of a family relationship.”
It added: "While we acknowledged that applicants were not required specifically to submit 'proof of address' (as referenced by the complainant), some were required to submit further documents beyond those stated in the ad.
"We considered that the actual proportion who were asked to submit further documents was likely to go beyond what the audience was likely to understand from the claim.
"In that context, we considered that the ad did not make sufficiently clear that, in some cases, applicants would need to supply documents beyond their passport or ID card.”
The ASA ruled the advert must not be broadcast again in the form complained about, adding: "We told the Home Office to ensure they made sufficiently clear that some applicants to the EU Settlement Scheme would need to provide additional documents beyond their passport or ID card.”
A Home Office spokesman said: "We completely disagree with the ASA's decision.
"The campaign was factual and complied with all necessary clearance processes for radio advertising.
"The campaign has had a positive impact and encouraged more than one million successful applications so far.
"The scheme is free, straightforward and EU citizens and their family members have plenty of time to apply.
"All they need to apply is their passport or ID card and to complete an online form."