The price of petrol at the pumps is rising again after weeks of falls.
The average cost of a litre of petrol is now 132.18p, with diesel at 137.26p, the AA said.
Average petrol prices peaked at 142.48p a litre in mid-April and were as low as 130.81p at the beginning of this month, before going up again.
But the AA said that had the fall in the north west European wholesale price of petrol been fully passed on to consumers, motorists would have been paying even less for fuel than they were at the beginning of the month.
Now, wholesale prices have gone up again, with market speculation which inflated prices earlier this year re-emerging, the AA said.
It added that Londoners appeared to be enjoying an Olympic fuel price boost.
Prices in the capital are usually among the most expensive in the country but, at 132.0p now for petrol and 137.2p for diesel, are not only lower than the UK average but not far off prices in the Midlands and the north of England.
Across the UK, petrol is cheapest in Yorkshire and Humberside at 131.6p a litre and most expensive in Northern Ireland at 133.4p.
South East England is dearest for diesel at 137.8p a litre and is cheapest in Yorkshire and Humberside at 136.6p.
AA president Edmund King said: "This week, we have seen UK inflation for June fall very close to the Bank of England's target.
"It makes you wonder how much closer it would have got had the full extent of lower fuel costs been passed on to drivers.
"Additionally, after the massive boost lower pump prices have given to family budgets and non-fuel consumer spending, it would be extremely disappointing if much of the benefit is lost to commodity speculation."
He went on: "It was inevitable that pump prices would eventually rise again but, as has been the case so many times in recent years, the questions remain: should it be happening now and what is driving them up?
"Is it the fundamentals of supply and demand or speculation in the oil and wholesale fuel markets? Current evidence seems to suggest the latter."