"Let no one be in any doubt: the rules of the game are changing." This was Tony Blair's warning on August 5, announcing a crackdown on Islamist extremists. That crackdown began to take shape yesterday, when the home secretary published a list of "unacceptable behaviour" that will provide grounds for the deportation or exclusion of foreign nationals from the UK. Yet while the deportation of so-called "hate preachers" may be a visible way for the government to signal its resolve, it must avoid pandering to outdated assumptions about the nature of the terrorist threat facing Britain.

Some of the measures proposed by the home secretary may be sensible. For example, the automatic vetting of individuals who have engaged in the activities listed before they are allowed to enter the UK looks prudent. Other proposed measures, however, are vague and even alarming.