UK Nationals who go overseas to join terrorist groups could now face up to 10 years in prison if they try to return to Britain.
The new laws will apply to future cases but not to those who have already left.
It comes as efforts to combat recruitment by Jihadi organisations.
British Security expert Margaret Gilmore said it should make it easier to get convictions for people who change their minds.
Ms Gilmore said: "If you turn up at the border, and say 'look, I was brainwashed, I was sent under duress, I didn't want to stay there, I've changed my mind, in the future that will not count."