Now Tories want us to pay for parking at the supermarket

David Cameron says the move would encourage families to use small shops on the high street and curb the growing power of food giants.

The Tories claim it would also help the environment because shoppers would ditch their car and use public transport.

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But it will dismay parents who have no choice but to use large supermarkets for their weekly shopping, especially in rural areas.

The idea is the latest policy to emerge from the Tories' Quality of Life group, headed by millionaire eco-warrior Zac Goldsmith and former Environment Secretary John Gummer.

It contains measures to encourage environmentally-friendly behaviour including higher taxes on gas-guzzling cars and jet travel and a clampdown on plasma TVs.

Mr Cameron gave his clear backing to the report in a speech yesterday when he committed a Tory Government to green taxes to 'discourage bad things'.

He said environmental taxation would be introduced only to pay for tax cuts elsewhere and insisted there were no plans for 'stealth taxes'. Charges for supermarketcar parking already apply in some inner-city areas to ease congestion but the Conservatives would expand it to target stores in the countryside.

Councils would impose the charges, spending the money on public transport or recycling schemes.

The proposal to tax shoppers has a high chance of becoming party policy after Mr Cameron last year launched an attack on Britain's 'big four' supermarkets - Tesco, Asda, Sainsbury's and Morrisons - which he said were developments.

The report says: "This is not only in the interest of protecting smaller local shops, but also to maintain the town's economic and social viability, reduce car dependency and promote 'walkability'."

In his speech to the London School of Economics yesterday, Mr Cameron said research shows that environmental taxes make more economic sense than other green measures such as carbon emissions trading schemes, where trees are planted to offset the amount of pollution created.

He added: "As taxes will always have an incentive effect - discouraging whatever they are levied on - why not use them to discourage bad things rather than good things?"

Tory MPs will be privately alarmed that the plan will be a massive vote-loser for their constituents.

Matthew Elliott, chief executive of the Taxpayers' Alliance, said: "A supermarket car park 'stealth tax' would be a big mistake. Families up and down the country rely on them for their weekly shop and it's often massively impractical to travel there by public transport."

Chief Secretary to the Treasury Andy Burnham said: "The truth is the Tories would need to raise green taxes by eye-watering amounts to meet the tax proposals they have been making."