Suspected jihadists, including an associate of hate preacher Anjem Choudary, tried to pose as illegal immigrants to sneak out of the UK undetected and head for Syria, it is understood.
Two suspected terrorists were discovered in the back of a lorry attempting to leave Dover and hiding among a group of illegal immigrants.
The men were among five people arrested by counter-terrorism officers and are suspected of trying to head to Syria to join fanatics there.
A third man was arrested also trying to leave Dover later and the remaining two, who were detained in London, are suspected of trying to help them.
It is understood one of those found in the lorry is an associate of Mr Choudary and was one of nine man, including the preacher, who were arrested in September as part of an investigation into Islamist terrorism.