Gordon Brown’s proposed international energy summit in London has been cancelled after Opec threatened to boycott it, The Times has learnt.

Mr Brown called for the meeting of heads of state of oil producing and consuming countries to be held in London on December 19 as a follow-up to a meeting held in Jedda, Saudi Arabia, in June.

However, in an interview with The Times, Abdullah al-Badri, the Opec Secretary-General, said that the cartel of 13 nations, which between them produce 40 per cent of the world’s oil, had threatened to boycott the event unless an invitation was extended to all the heads of state of individual Opec member countries.

These include President Ahmadinejad of Iran, as well as President Chávez of Venezuela and Colonel Muammar Gaddafi, the Libyan leader.

It was unclear yesterday if such an invitation was ever offered, but a spokesman for the Department for Energy and Climate Change confirmed that plans for the summit had been dropped. Instead, he said that Ed Miliband, the newly appointed Energy and Climate Change Secretary, would host a ministerial-level meeting to discuss energy matters in London around the same date.

The spokesman claimed that the decision to abandon the summit had been taken because world leaders were too busy dealing with the fallout from the financial crisis to attend. But it was no secret that the proposed meeting, which Mr Brown had said he hoped would form part of a new initiative designed to improve the level of dialogue between oil producers and consumers, was proving to be a diplomatic minefield to organise.

While he declined to identify which, Mr al-Badri said that some member countries had informed Opec that their heads of state had not been invited. The British government spokesman declined to comment on which Opec leaders had received invitations, although he said that some had been sent out in August.

Mr al-Badri said that the Opec secretariat, which he heads, would not participate unless all the heads of state were invited. “The meeting [in Jedda] was called because prices went out of control but, in my opinion, there should be no follow-up,” he said.

He added that an alternative organisation already existed for dialogue between oil producers and consumers, the International Energy Forum based in Saudi Arabia.

The Prime Minister did not endear himself to Opec this month when he said that it would be “absolutely scandalous” for the organisation to consider a production cut to support global oil prices at a time when the global economy was rapidly weakening.

On Friday Opec did exactly that and slashed production by 1.5 million barrels per day in an effort to reverse the fall by more than half in crude prices since July 11, when they touched a record high of $147 a barrel.

The cut has so far failed to arrest the rapid fall in prices. Yesterday crude prices slumped to fresh 17-month lows below $62 a barrel.

The AA said yesterday that average petrol prices had dropped below the £1-a-litre level over the weekend for the first time in almost a year.

In Sunday trading the cost of petrol fell to 98.63p per litre, with diesel 111p, taking the price of petrol back to where it was around October 30 last year. Compared with the record high price of 119.7p per litre in mid-July, this has put about £45 a month back into the budget of a family with two petrol-driven cars.

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