Newly re-elected Conservative Prime Minister David Cameron, in order to please anti-EU constituents who were essential to his re-election, promised a referendum on EU membership by 2017, although it could come sooner than that.
At the same time, the promised referendum is again inflaming secessionist sentiment among Scottish nationalists and separatists who wish to remain a part of the EU.
Naturally, it would be highly simplistic to point to the EU issue as the only major issue behind the Conservative victory. As Louis Rouanet points out here, the British economy in recent years has performed relatively well — with an emphasis on the word "relatively" — and has done so by eschewing the French model of tax hikes and increased interventionism. Whether deserved or not, Cameron was probably able to convince more than a few voters that he deserved some credit for this.