Virgin Media has been asked to change an advert in which it claims to offer broadband users "unlimited downloads".
Although small print did carry the notification that heavy users are liable to be capped during peak hours, the Advertising Standards Authority (ASA) decided that the notice was not made clear enough.
"We considered that the 'unlimited downloads' claim was a significant factor likely to influence consumers' purchasing behaviour and the condition attached to it, a traffic management policy at peak hours, should, therefore, be made apparent," the ASA explained.
Virgin Media is now required to include a link to the small print in the relevant text, so customers are in no doubt as to the details.
The provider launched its fibre-optic broadband network last year, offering access to connection speeds of up to 50Mb.