BT, Virgin Media, TalkTalk and Sky are among a number of ISPs that have agreed to reveal how and why they slow web users' connection.

The ISPs have signed a code of practice, which was drawn up by the Broadband Stakeholder Group (BSG) and requires them to explain why they need 'traffic management policies', when they take place, how long they last and whether certain online activities are given priority over others.

"This commitment to provide clear and comparable information in a common format is very important," said Anthony Walker, chief executive of the BSG.

"It will not only help to ensure consumers are better informed about the services they buy and use, but will also provide a clearer picture for policy makers of the way in which traffic management is actually used in the UK market."

The majority of UK ISPs use 'traffic management' in a bid to ensure that during busy periods their networks are not overloaded. Less critical activities such as sending emails and downloading files are delayed to ensure other tasks, such as streaming video, are smooth and uninterrupted.

However, a number of concerns have been raised that the move could lead to a two-tier internet that will see firms paying to ensure web users can access their content and apps without being subject to traffic management policies.

"We recognise that there are certain types of traffic shaping that need to occur in order to maintain the integrity of the network," Jeff Lynn from the Coalition for a Digital Economy (Coadec) told the BBC.

"But we see that as very different from developing business models in which a particular ISP takes money from 4 on Demand [for example] and makes it easier to download 4oD videos than it does BBC videos."

The ISPs will be joined by O2, Three and Vodafone in trialling the practice. A report looking at how successful the code is will follow after 12 months.