Sales of child car and booster seats have soared ahead of new rules which make them compulsory for all children up to 12 years, retailers said today.

Halfords has sold double the volume over the last two months compared to the same time last year.

Supermarket chain Asda reported a 387 per cent year-on-year surge of all types of car seats.

From Monday, any youngster up to 12 or shorter than 135cm (approximately 4ft 5ins) will have to use a child seat or booster - even if they have already spent several years in adult seats.

Tesco said sales of its booster seats - which are suitable for bigger children - were up 1,000 per cent this week compared to the same time last year.

Prices of car seats and booster seats at Tesco range from around £30 up to £150.

Halfords has geared up for the new law with a huge publicity drive to alert parents.

It also put child measuring devices in its 400 UK stores to illustrate the new requirements.

The chain's head of PR Barbara Cadd said: "Sales have doubled and they are still rising.

"We knew there was going to be massive demand for these so we ordered several thousand seats more than we would have done last year."

She warned that child car seats should be properly fitted by a trained member of staff.

Asda is calling on the Government to drop the VAT on car seats to help parents who will be obliged to buy them.

The supermarket chain said it was dropping its own prices by about ten per cent to cover the cost of the tax.

Asda's health and beauty director David Miles said the new legislation means parents will face a "huge" expense.

He said: "Asda would like to see VAT scrapped on child seats and is doing its bit by rolling back the price of all car seats to make them more affordable. We think the Government should also help reduce prices and end VAT on child car seats."

The new rules apply to children travelling in cars, vans and goods vehicles.

Exceptions to the new laws are when children travel in the rear seats of taxis or during short emergency journeys - which does not cover school runs.

There is also an exception for a third child travelling in the rear when the vehicle has room for only two booster seats.

Breaking the new law will lead to a £30 on-the-spot fine for the driver, or a maximum fine of £500 if convicted in court.

The new measures aim to cut child deaths and injuries in road accidents.

Despite the strong sales figures, a recent poll by Mother and Baby magazine showed that one in three mothers were still unaware of the new laws.