Virgin Media has been censured by the advertising watchdog over an advert claiming high download speeds.
After a complaint brought by competitor BT, the Advertising Standards Authority (ASA) found a Virgin advert breached rules when showing download speeds.
The 'Hate To Wait' advert claimed a TV show on the firm's M package could be downloaded in 26 minutes.
BT claimed the advert was misleading as Virgin capped customers' speeds during peak hours, so download speeds for songs and TV shows were inaccurate.
The ASA found the ad did not make it clear this download speed was only possible in off-peak times.
Also a 30-minute TV show of 341 MB would automatically breach the M package download limits of 300 MB.
Virgin claimed its 2Mb package was largely used by people simply browsing the internet and so they would be unaffected by any download caps.
The firm explained customers on the faster 20Mb package would face such limits as they typically uploaded and downloaded more files.
Virgin added the figures quoted in the advert were accurate when all its systems were working fully and argued that that was clearly stated in the footnoted text.
Last month Ofcom brought in a new voluntary code for the broadband industry following a serious of complaints.
Firms will still be allowed to advertise broadband speeds of up to a certain amount, which are often not reached as they represent the very maximum possible internet speed.
However, before a customer signs up they will have to carry out a speed test to determine the actual download rate.
John Carter, a spokesperson for BT, explained the firm was not "hiding behind" promises of speeds up to a certain level.
"There are physical constraints so it is very difficult to give an average speed. We try to be as transparent as possible."