Petrol prices are set to rise a further 3p per litre thanks to an increase in wholesale prices and a weakened pound, according to the AA.
This comes after a 5p-a-litre price surge in the last month, and coincides with latest figures that show petrol sales have slumped to their lowest in over 20 years.
Fuel prices have seen a 1p increase in the last five days alone.
Motorist's misery may be worsened if George Osborne's plans to raise duty go ahead in next month's budget. The average cost of petrol in the UK is now 138.32p a litre, with diesel rising 4.78p since mid-January to hit a UK average of 145.10p.
The squeeze on motorists has led to many turning their backs on the car, with the latest figures showing monthly sales have fallen 14 million litres since last month to 1.465billion litres, the lowest since government data began in 1990.
The AA said currency speculators betting against the weak pound and soaring wholesale prices has led to the prices increase.
AA president Edmund King said: "This latest surge in fuel prices and its impact on spending indicates that UK drivers and families can't take any more.
The AA is also urging the Chancellor, who froze duty rises in March 2011, to halt the planned increase.
"Given the lashing motoring families and UK businesses are taking from speculator-driven fuel prices, we hope the Chancellor spells out clearly in the forthcoming Budget that he can feel the pressure on families and business, and that he will cancel the September rise if that strain is too great."