In many of the marginal seats that Conservatives have to win to gain an overall majority in 2015, trade union members could hold the balance of power. (conservativehome.blogs.com)
Parliament is hung, with no individual party gaining an overall majority. (independent.co.uk)
It's often said in UK politics that the Conservatives usually require a 7 percent lead in the popular vote to gain an overall majority of seats in the House of Commons; but the Labour party can get a majority with practically no lead at all (indeed it's not inconceivable that the Conservatives could have a small plurality of votes and Labour still have a majority of seats). (politics.stackexchange.com)