Prime Minister warns retailers to cut prices to below £1 per litre, or else face investigation.

If you’re buying petrol today, shop around. The wholesale price of oil fell yesterday of $71 a barrel, the cheapest it has been for 14 months. And while the petrol supply industry says that it takes around six weeks for changes in world market prices to reach forecourts, wholesale prices have been dropping for some time and the changes have filtered to the pumps only slowly.

A survey run by shows that 95% of visitors to the site believe that petrol prices have dropped too slowly. That’s typical of the mood across the country, and Prime Minister Gordon Brown has said petrol prices must drop, or firms could face an enquiry.

Supermarkets who sell petrol have taken a lead and dropped the price of unleaded to 99.9p per litre, and diesel to 110.9p. But major petrol retailers have as yet kept prices well above £1 per litre, except for sites close to supermarket forecourts. Average prices, according to the web site, are currently 106.7p for unleaded and 117.7p for diesel.

‘The public knows that when oil prices go up, it is reflected very quickly in the pump price,’ Said Mr Brown. ‘What we want to know is that when oil prices come down, that is also reflected in the pump price.’

His words are a marked shift in tone: previously Mr Brown has been reluctant to take such a stand. While he has no formal power to order price reductions, he is clearly hinting that a competition inquiry could happen should petrol retailers fail to take notice.