She said there was a review under way into the possible reform of Vehicle Excise Duty.

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Its chairman, David Begg, wants to explore whether road pricing could replace vehicle excise duty and petrol duties.

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But what if half the country's cars are exempt from Vehicle Excise Duty?

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Under the two-tier plan, part of a driver's Vehicle Excise Duty payments would go to private companies managing and investing in the road network.

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British hauliers, who face similar charges when their lorries travel in the EU, will also have to pay the UK levy, but vehicle excise duty will be cut to compensate.

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Some of the benefits are well-known, such as the lack of Vehicle Excise Duty and exemption from the London congestion charge, but it's becoming easier to charge up a Nissan LEAF on the move with more public charging points opening all the time.

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