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

Mr Brown wants the December meeting to be a success but assembling the guest list is proving tricky. So far only Mahmoud Ahmadi-Nejad, the president of Iran, appears to have been blackballed among the leaders of big oil producing states.