NEW car tax regulations have forced up the price of some popular family diesel cars by more than £300, according to analysis by online sales company BuyaCar.

The price of many mainstream new diesel cars leapt on April 1 as manufacturers passed on the cost of the Chancellor's latest tax increase on the most modern diesel cars.

The diesel surcharge adds between £15 and £520 to the cost of taxing a car in its first year.

Many car retailers pay the fee on behalf of buyers, which is why prices have gone up to reflect the extra cost.

However, motorists can dodge the diesel tax, which applies only to brand new cars from the beginning of April.

Pre-registered diesel cars, which typically have only a handful of miles on the clock, are not subject to the new tax - and are usually available with additional discounts - as long as they were registered and given a number plate before the end of March.

The savings on pre-registered family cars can run into thousands of pounds, including the tax.

For example, the new price of a petrol Ford Kuga Titanium 1.5 T EcoBoost rose by just £30 from April 1, but the diesel equivalent model went up by £315.

In the case of a Ssangyong Korando the petrol model price remained unchanged while the diesel equivalent version rose by £350.

The change was even more stark for buyers of the diesel Mercedes E-Class with an E350d AMG Line now costing £440 more, while the price of the petrol E350e AMG Line remained unchanged.

Only last month BuyaCar.co.uk revealed that many consumers are already bypassing new cars in favour of massive savings already available on cars sporting the new March plate.

Those cars are being pre-registered by dealers to sell as used cars, so they can hit new registration targets.

The online motor retail specialist now says that the new tax hike on diesels is likely to boost interest in pre-registered diesel cars even more.

BuyaCar managing director, Austin Collins, said: "With new diesel sales still on the way down, but used diesels still popular, we foresee customers searching out the greater savings available with pre-registered and nearly new cars.

"Cars sporting the brand new March 18-reg plate were already on sale by the middle of last month, so it's clear that there are plenty of deals available, offering substantial savings."

The diesel surcharge was announced in last year's Budget and affects the tax paid on brand new vehicles, which is based on carbon dioxide emissions.

All diesel cars move up a tax band, which increases the cost of tax by between £15 and £520.

The surcharge applies only for the first year, after which owners of petrol and diesel cars pay a standard annual rate.