The average price of diesel is “perilously close” to £2 per litre, motorists have been warned.
Figures from data firm Experian show the average price of a litre of diesel at UK forecourts reached a new high of 197.1p on Tuesday.
The average price of petrol was a record 189.3p per litre, which the AA branded “a disgrace”.
Twelve months ago the prices were 133.5p for diesel and 131.1p for petrol.
The Competition and Markets Authority announced last week that it will carry out a “short and focused review” of fuel prices after a request by Business Secretary Kwasi Kwarteng.
Car use increased on Tuesday due to 80% of train services being cancelled because of industrial action.
Mr Williams said the price of diesel is “perilously close to the £2-a-litre milestone”, with the cost of a full tank for a 55-litre family car exceeding £108.
He went on: “With the oil price falling and wholesale costs down over the last week, pressure is mounting on the biggest retailers to turn the tide and put petrol pump prices into reverse.
“It now seems we’ve reached the current petrol peak, so we expect to see the big four supermarkets start to cut their prices.
“As they dominate UK fuel retailing this should lead to others reducing their prices too, which will benefit drivers everywhere.
“The situation with diesel is different, unfortunately, as wholesale prices last week still put it on course to move closer towards an average of £2 a litre.
“If, however, oil continues to trade lower it could just prevent this from becoming a reality.”
AA fuel price spokesman Luke Bosdet said: “With petrol continuing to set new records more than a fortnight after the wholesale price started to fall, today’s new record is nothing short of a disgrace.
“Rush-hour travellers who might have taken the train are being forced into their cars by the strike, particularly for local journeys.
“To add to their woes, the fuel trade is either on a deliberate collision course with the Government or they just don’t care.
“The Competition and Markets Authority has launched its probe into road fuel prices and, with previous investigations coming out in favour of fuel companies, the trade probably thinks the same will happen this time.
“The AA and its 13 million members hope that the competition watchdog will dig deep into what is going on with these crippling and unjustified pump prices.”