Alissa Cooper, formerly at CDT and now at Cisco, wrote her PhD dissertation on network neutrality practices in the US and the UK. Here is an interesting tidbit from her abstract:
Competition promotes rather than deters discrimination because it drives broadband prices down, encouraging operators to manage high-volume applications whose traffic incurs high costs. Regulatory threat can be sufficient to counteract these desires, but in its absence and without concerns vocalized by interest groups, discriminatory approaches endure.
In many European countries, unbundling has lead to competition among providers. While this has put downward pressure on consumer prices, investment in the backbone is far lower. Altogether, these industry features often lead companies pricing data since their margins are low, thus leading to very schemes that network neutrality advocates deplore. Practically speaking, this is why Europe has had far more problems with network neutrality than the US.