Treasury minister Ed Balls has challenged the Conservative Party's green tax plans for failing to give details of how it will implement them.
Earlier, George Osborne, the shadow chancellor, declined to spell out any detail, but committed a future Tory government to raising the share of revenue raised by environmental taxes.
Balls, the Treasury minister, asked Osborne to say whether taxes on motorists should rise when petrol prices were so high.
He added: 'If you are going to be a serious opposition you need to come along and say what are your proposals, how would you pay for them, and until then people won't take you seriously.’
