From April, the price of tax discs will soar for owners of cars with engines of 1.6 litres or more, due to new vehicle excise rates.

Retired Riber farmer John Mumby said many Peak District farmers were unaware of the new laws and would be surprised when they came in.

Mr Mumby said the rates were designed to target "Chelsea tractors", but would hit farmers hard.

Mr Mumby said: "Farmers still need big cars – they can't just get a little one and see if that's going to pull a three-tonne trailer.

"I spoke to quite a few farmers at Bakewell Market and not one of them knew about the changes", he added.

"Everybody's struggling and this is just another kick in the teeth."

By 2010, owners of high-powered Land Rovers will have to pay up to £450 more than now. The new rates will apply to all cars registered since March 2001.

Dales members of the National Farmer's Union were unhappy with the duty.

Alison Pratt, from NFU East Midlands, said: "It's something members have raised, the Bakewell branch in particular, and I've sent information over there.

"For farmers these vehicles are their workhorses and are absolutely necessary," she added.

West Derbyshire MP Patrick McLoughlin said the excise duty would also hit families.

"I think a lot of people haven't worked out what the implications will be and won't be happy – it's not just farmers."

But the Treasury said the new excise rates were easier to understand, would benefit owners of carbon-efficient cars and encourage people to buy environmentally-friendly vehicles.

A spokesman said: "The cars that use more oil will need to pay more – that doesn't necessarily mean farmers will be hit.

"The point is we already have graduated bands to reward people for driving environmentally-friendly cars and people will be able to take a choice," he added.

For a full list of the vehicle excise duty rates click here.