At present most ISPs employ Traffic Management or Traffic Shaping as a perfectly acceptable means to balance the performance of their networks, which allows the majority of customers to avoid being unfairly affected by a minority of heavy users. This is often done by restricting internet traffic (speed) to busy services (e.g. P2P) or more generally at peak times of day.
Many ISPs prefer the above method to either raising prices or being more realistic about their usage allowances. Sadly some operators are known to restrict certain services, such as VoIP (e.g. Skype) and P2P (File Sharing), to such an extreme that they are no longer usable. Similarly a number of operators have IPTV services, such as BT and TalkTalk, which require flexibility in order to favour content from specific providers.
The Government Will Not Tell Us What To Do: “Forcing ISPs to carry all traffic infringes on freedom of speech”