With elections in the UK just six months away, David Cameron is going on the offensive: "We want to create the toughest system in the EU for dealing with abuse of free movement" and "reduce the current exceptionally high level of migration from within the EU," he said on 28 November. This renegotiation – a condition, if he is re-elected, for defending Britain's continuing EU membership in a possible referendum in 2017 – implies a treaty reform . Cameron is…