Gordon Brown is to invite Colonel Muammer Gaddafi, Libya's leader, and Hugo Chávez, the president of Venezuela, to London to attend an international oil summit which is turning into a diplomatic headache.

Mr Brown wants the December summit to be a success, but the guest list is proving tricky. So far only Mahmoud Ahmadi-Nejad, the president of Iran, among the leaders of big oil producing states appears to have been blackballed. The prime minister sees the event as a chance to co-ordinate the world's response to rising oil demand, while proving to a domestic audience he is taking action to hold down fuel prices.