Islamic State is "plotting Christmas terror attacks across Britain and Europe," according to a MI6 chief.
Daesh is "looking to avenge" the publication of the controversial cartoon based on Prophet Muhammed (PBUH) in France, says the top spy.
Aimen Dean claims plots are being hatched to terrorise Europeans this winter.
Mr Dean spent eight years spying on al-Qaeda before his cover was blown by a US intelligence leak, reports Mail Online.
Speaking at a security conference in London, Mr Dean warned that ISIS commander Abu Omar al-Shishani has planned to send extremists to Europe, through Turkey.
Members of the group will travel across the Mediterranean from North Africa, he added.
He warned Daesh members will carry out attacks before Christmas while lockdown eases in Britain, Germany and France.
It comes as earlier last month Britain's terror threat level was raised to '‘severe’ after a string of attacks across Europe.
Priti Patel confirmed the change which meant it it is highly likely there could be an attack in the UK following atrocities in France and Austria.
Mr Dean told the International Security Week conference: "The worry is that, according to people who know him, [Shishani] is planning to avenge the Prophet Mohammed (PBUH) cartoons in places like Germany, UK, France and all around Christmas time.
"I'm afraid I'm not bearing good news but we need to be worried about the wave of terror that is coming from northern Syria and Libya for Christmas this year.'
He added: "This promise of no lockdown at Christmas has made it a more attractive timeframe for targeting. Already they have been thinking about it, already they have been looking at it and I feel this will be the next target."
In October a teacher was beheaded in Paris for reportedly showing a cartoon of nude Prophet Mohammed (PBUH) to his class.
Samuel Paty, 47, was said to be "concerned for his safety" in the days leading up to his gruesome killing.
French President Emmanuel Macron released a statement after the attack and warned against "Islamist separatism" and announced mosques would be placed under further state control.