The price of petrol has broken through the 140p-a-litre barrier for the first time.

The average price at the pumps has now reached 140.20p a litre, with diesel at a new record of 146.72p, the AA said.

Petrol prices have now risen more than 2.75p a litre in just three weeks, while the cost was only 132.25p a litre at the beginning of the year.

The price of diesel at the start of 2012 stood at an average of 140.56p.

The AA said that for the owner of a car consuming, on average, 106.17 litres of petrol a month, this year's 7.95p-a-litre increase in petrol has added £8.44 to the monthly fuel bill.

In the Budget, Chancellor George Osborne said the fuel duty rise planned for August, which with VAT added will amount to 3.62p a litre more for road users, would be going ahead.

The AA said that this rise would mean monthly petrol costs would, by August, have increased by more than £12 since the start of the year. The AA added that at current prices, this would slash two-thirds of the £18.33-a-month (£220 a year) increase in the personal allowance set out in the Budget.

RAC technical director, David Bizley, said: "Just days after the chancellor refused to cancel the planned August rise, prices have now hit another painful barrier for Britain's hard-pressed motorists. A figure of £1.40 a litre is a massive price for people to have to pay and there is no end in sight to rising prices. The way things are going the planned duty rise will see average petrol prices hit the £1.50-a-litre mark - forcing more and more people who need their cars off the road."

Labour Treasury spokeswoman Cathy Jamieson said: "Hard-pressed motorists and businesses are being hit hard by record petrol prices. But there is still no sign of the fair fuel stabiliser the Chancellor promised in last year's Budget. It shows just how out of touch George Osborne is that, in the Budget, he said he could afford to give a huge tax cut to people earning over £150,000, but couldn't afford to cut fuel duty for middle and low-income families feeling the squeeze.

"Drivers already facing record petrol prices are now facing a 3p rise in fuel duty in August. Labour's five-point plan for jobs includes a temporary VAT cut which would immediately take 3p off the price of a litre of petrol and jump-start our stalled economy."