The increase in mass downloading caused by things such as the BBC's on demand TV iPlayer (why does everything have to begin with an 'i' these days?) is putting strain on the networks apparently.
I don't even understand why the ISPs are arguing. The network is core to their business, if the network can't take it then they have to upgrade it at their cost. The problem is their own fault, they sell 'unlimited' broadband, people use it, full stop. If 'unlimited' wasn't meant to include TV on demand then they clearly need to get better at predicting the future or at least be more careful about what they offer.
More multimedia, TV, films, legal downloading isn't something that's snuck up on the world. It's been inevitable since broadband was first introduced.
Maybe in the future they'll have to change their offerings and remove the 'unlimited' broadband option. That's fair enough. If you want to store ten boxes with a storage company it will cost you more than storing two. If you want to regularly fill up your swimming pool from the tap the water company will charge you accordingly. For the time being though they're going to have to live with it.
In the US this change from the 'unlimited' broadband offering has led to worries about ISPs prioritising content (i.e. such as blocking people from file sharing regardless of the files) and threatening 'net neutrality' (a phrase I've never heard before so see definition below).
Net neutrality = 'A broadband network free of restrictions on the kinds of equipment that may be attached, on the modes of communication allowed, that does not restrict content, sites, or platforms and where communication is not unreasonably degraded by other communication streams would be considered neutral by most observers.' (source: wikipedia)
The difference here though is that the US broadband market consists of 2 major providers. If anyone tried to do this in the UK users would just move to another of the 60 different ISP providers (I'd hope).
I say let the ISPs try and charge the customer, or try and sell packages based on internet usage. As long as there is a free (ish!) market and the ISPs don't all band together in a cartel, the competitive nature of the UK broadband provider market will mean that consumers will choose what they want...