The Advertising Standards Authority (ASA) has ruled in favour of BT after it challenged a claim made in a Sky broadband advertisement.
A press ad, seen in May 2015, claimed that it offered the "fastest peak time speeds measured by Ofcom", with the text underneath saying this is the case for speeds up to 38Mbps.
The small print at the bottom of the ad then read "... Fastest peak time speeds: measured by Ofcom comparing Sky, BT, Plusnet and EE's up to 38Mb in its latest UK fixed-line broadband performance report (November 2014) ...".
BT took issue with the claims on the grounds that the Ofcom report cited by Sky had not taken into account Wi-Fi performance.
Furthermore, it argued that the Fibre-to-the-Cabinet data used in the report had not been normalised to account for the distance from the exchange.
BT believed these factors meant that the ad was misleading, although Sky insisted this was not the case, saying it factually reported the data and did not infer wider performance claims requiring further substantiation.
Sky also pointed out that Ofcom's reporting methodology was designed to enable consumers and industry stakeholders to make like-for-like comparisons in relation to broadband speeds.
In addition, it argued that it would be unusual for advertisers to be prevented from factually reporting on a consumer report published by a sector watchdog to enable objective comparisons.
Sky did subsequently amend the footnote qualification to make it clear beyond doubt that Ofcom excludes Wi-Fi performance, as this "varies by device, home environment and ISP".
However, the ASA ultimately decided that the ad had not made it clear that the "fastest peak time speeds" claim related to fixed-line broadband performance only and that the claim was misleading.
"We considered it was not sufficiently prominent and did not make sufficiently clear that Wi-Fi performance was not included in the analysis," it stated.
The regulator therefore ruled that Sky must not show the ad again in its current form.
"We told Sky UK Ltd to ensure that in future they made clear that speed claims related to fixed-line performance only, if that was the case," the ASA concluded.