On Wednesday, the RAC said filling up a family car costs £99.40 as a result of petrol prices having made their biggest daily jump in 17 years.
A rise of more than 2p a litre has increased the average price of petrol to 180.73 per litre.
Before the most-recent big increase on Tuesday, the price of petrol stood at 175.6p per litre.
Meanwhile, a diesel-run car with a fuel tank of 55 litres would cost £102.61 to fill up, after the average price of diesel rose by almost 1.5p to a record high of 186.57p per litre.
The increase in prices has reportedly been driven by Russia’s invasion of Ukraine and Europe’s moves to reduce dependency on Russian oil.
RAC fuel spokesman Simon Williams said: “A full tank of unleaded has now shot up to £99.40, moving us ever closer to the milestone £100 petrol fill-up – an unfortunate landmark we may reach as soon as today.
“Asda hiked its average petrol price nearly 5p a litre in a single day, which is unheard of. These are unprecedented times in terms of the accelerating cost of forecourt fuel.”
Motoring groups are concerned that the 5p per litre cut to fuel duty announced in March has not been passed on to customers.
AA spokesman Luke Bosdet said: “Yesterday’s more than 2p-a-litre leap in average UK petrol prices is a huge shock, and fuels concern that speculation of a £2 litre just gives the fuel trade licence to pile on extra cost and misery.
“The government needs to act fast to rein in these excesses.”
Downing Street has indicated that petrol stations that fail to pass on the fuel duty cut could be named and shamed.
On Wednesday, PM Boris Johnson’s official spokesman said the government was “not confident” that the failure to pass on the savings was happening at all petrol stations.
But, he added, the Competition and Markets Authority (CMA) has the power to launch an investigation – that ministers would support – into whether the duty cut has been passed on.
He said the government was “continuing to look at all possible options” and “transparency may have an important role to play” in making sure customers were benefitting from the fuel duty cut.
Tory MP Robert Halfon urged the government to set up a new regulator to “force proper competitive and fair behaviour from the oil companies so motorists are not ripped off” and said a windfall tax on wholesalers should be considered.
The chairman of the Commons Education Committee told BBC Radio ’s PM programme: “The fact is the oil companies, the wholesalers, are fleecing the motorist.
“It may be the government could consider windfall taxes on the people providing the petrol and diesel wholesale, but the crucial thing for me is setting up a new regulator called PumpWatch.”
Some forecourts are already selling petrol above £2 per litre.
Price comparison website PetrolPrices said the most expensive price was 202.9p per litre at BP sites on the A1(M) near Sunderland, Tyne and Wear; the A1(M) near Wetherby, West Yorkshire; the M4 near Chippenham, Wiltshire; and the M6 near Burton-in-Kendal, Cumbria.
The most expensive petrol stations on local roads are selling petrol at up to 196.9p per litre in Glasgow and near Stafford, Staffordshire.
Additional reporting by PA