Speaking in an interview conducted before the vote in parliament, the result of which had been widely anticipated, Assad said Cameron`s strategy would make the situation worse, not better.
"They are going to fail again," he said. "You cannot cut out part of the cancer. You have to extract it. This kind of operation is like cutting out part of the cancer. That will make it spread in the body faster."
Police in London said they were treating a stabbing on Saturday as a terrorist incident after a man wielding a knife slashed another, screaming according to British media "this is for Syria".
Assad ridiculed Cameron`s assertion that there are as many as 70,000 Western-backed opposition fighters in Syria who would open a political solution to the civil war and could retake territory from jihadists weakened by the air strikes.
"This is a new episode in a long series of David Cameron`s classical farce ... where are they? Where are the 70,000 moderates he is talking about? There is no 70,000. There is no 7,000."
Cameron opposes Assad`s government in Syria, where the more than four-year civil war has forced millions of refugees to flee the country. In 2013 Cameron failed to win parliamentary approval for air strikes on Assad`s forces.
Britain is part of an U.S.-led coalition conducting air strikes against Islamic State in Iraq and Syria, where militants have captured large areas and proclaimed a Caliphate to rule over all Muslims.
Cameron, setting out his strategy last week, said air strikes alone would not be enough, and that Britain was pursuing a multi-faceted approach designed to defeat Islamic State and deliver a political and humanitarian solution to the civil war in Syria.
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