Petrol in the UK could increase by 2p a litre in the short term, and more if the crisis continues, the RAC said.
RAC head of external affairs Pete Williams said: “The worsening situation in Iraq is causing a knee-jerk reaction in the global fuel market with wholesale prices going up one pence over Wednesday and Thursday. This uncertainty is being made worse as the warring factions advance on some of the oil facilities, particularly the city of Kirkuk.
“We anticipate that it is likely to push the pump price of both petrol and diesel by 2p per litre in the short term and this could well go much further.
“After a period of relative stability, and a welcome drop in the cost differential for diesel, this once again demonstrates how UK motorists and businesses are at the mercy of world events and the volatile nature of the global fuel market.”
Meanwhile, Britain has deployed a humanitarian team in Iraq to assess the needs of civilians fleeing the violent takeover of parts of the country by Islamist extremists, International Development Secretary Justine Greening has announced.
Ms Greening said the UK’s Department for International Development stands ready to provide “whatever help is needed” to assist the hundreds of thousands of people believed to have fled their homes in northern Iraq.
Foreign Secretary William Hague has made clear that Britain will not get involved militarily in the struggle between the administration of prime minister Nouri al-Maliki and jihadists from the Islamic State of Iraq and the Levant (Isis) group.
The al-Qaida splinter group took control this week of Iraq’s second city Mosul and Saddam Hussein’s home city of Tikrit as part of an effort to set up a Sunni militant enclave across the Iraq/Syria border.
Militants press on to Baghdad: Page 16