The unprecedented gathering, which the Foreign and Commonwealth Office insisted was not co-ordinated with any British officials, was led by Abdel Halim Khaddam, who predicted that Syria’s increasingly dictatorial leadership would one day soon be toppled by a popular revolt.

Speaking to The Times under tight security in a suite at the Dorchester in Park Lane, where the dissident National Salvation Front movement was launched, Mr Khaddam said that corruption and the abuse of power had alienated President Assad from his people.

“This regime is doomed. It has to use repression to stay in power, while the people go hungry and see the wealth stolen by the corrupt elite,” he said.

Mr Khaddam, 74, served as Vice-President for more than two decades and was once Damascus’s pointman in Lebanon, when Syrian security forces effectively controlled the country.

He fell out with the President last year after the assassination of Rafik Hariri, the former Lebanese Prime Minister, and after the ruling Baath Party failed to accept democratic reform.

The National Salvation Front claims that it has 75 prominent supporters from across the political spectrum, all of whom are exiles, including a representative of the banned Muslim Brotherhood.

Despite yesterday’s London meeting, observers believe that President Assad has strengthened his position in office over the past year. Last year he was under pressure from America and the West, and there were predictions that his regime would go the way of the Baathists in neighbouring Iraq.

But the leadership in Syria, dominated by the minority Alawite sect, has successfully presented itself as a force for stability in the region.

Mr Assad has re-established his authority in part by cracking down on opponents. Scores of dissidents have been arrested by the authorities, including Anwar al-Bunni, a lawyer, and Michael Kilo, a writer and one of the country’s best known human rights activists.

The one issue that could still threaten the regime is the UN’s investigation into Mr Hariri’s assassination, which has been widely blamed on Syrian intelligence officers working under orders from Damascus.

Mr Khaddam, who has given evidence implicating Mr Assad in the murder, said that it was unthinkable that the order to kill the former Lebanese leader would have been taken without the President’s knowledge.

“The assassination could not have happened without his [the President’s] order. In Syria the security apparatus is in the head of the President,” he said.

Since Mr Khaddam began speaking out against the Syrian regime he has been branded a traitor. Legal proceedings have begun against him and 24 other members of his family, including his wife, his three sons and daughter, who were all summoned to appear in court last month.

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