Sky Broadband has been ordered to pull a national press ad following a complaint from BT that it was misleading.
The ad was published in October 2017 and said "Get Unlimited Broadband At Our Best Prices".
However, BT argued that the claim was misleading and challenged whether or not it could be substantiated.
BT therefore complained to the Advertising Standards Authority (ASA), which was told by Sky that the prices offered were the best for the products advertised and that the ad made it clear they were based on conditions such as subscribers taking up Sky TV.
Sky also stressed that it did not claim the prices offered were its "best ever prices" and was making no comparison against prices it had charged in the past, or else it would have made this clear.
Despite this argument, the ASA upheld BT's complaint, saying the ad did not clarify the basis of the claim being made.
As a result, it ruled that consumers might understand the "Our Best Prices" statement to mean prices were lower than they had been for a "reasonable amount of time".
The ASA added that in the previous month, Sky had offered the relevant broadband product alone at lower prices, leading it to conclude that the ad "was likely to mislead".
Sky has therefore been told not to run the ad again in its current form and make clear the basis of its lowest price claims in the future.