The Advertising Standards Authority (ASA) has banned a broadband advert published by internet service provider 3.
3 was instructed to withdraw the advert - in which it claimed to be the "No.1 network for mobile internet speed" - due to concerns over the vague nature of the statement.
The claim was made based upon the findings of an independent YouGov Mobile Broadband report, but these statistics were not made available to the public for comparison.
"We considered the claims in the ad… were likely to be understood by consumers to compare 3 products and services with those of their competitors," an ASA statement read.
"YouGov could confirm the categories in which 3 had been ranked top but that was not made clear in the ad and further details of how the comparison was arrived at were not available."
Ofcom is currently undertaking a wider review of broadband speed advertising within the UK broadband industry.
The communications regulator has raised concerns that the headline speeds advertised for many broadband deals are only available to a minority of subscribers.