Gordon Brown, the British prime minister, is downgrading plans for an international oil summit and withdrawing invitations to George W. Bush, Hugo Chávez of Venezuela and Muammer Gaddafi of Libya after a collapse in oil prices sapped the interest of world leaders.

The move to “recalibrate” the summit to ministerial level comes after British ambassadors spent months selling the importance of the December conference, which Mr Brown called to address “the most worrying situation in the world”.