The publication of a list of behaviour and activities which may trigger deportation or exclusion from the UK has two purposes for the home secretary.
Deportation notices are likely to face legal challenges
It serves notice to specific individuals that their days here may be numbered.
And it sends a wider message to the British public that activity by extremist clerics and others, which has previously been tolerated by the government, is now, following the London bombings, considered beyond the pale.
But the list does not add to the home secretary's existing broad powers to deport under the Immigration Act 1971.
According to the Home Office, those powers have been exercised 14 times in the past year.
Twelve times on national security grounds and two on other grounds which make someone's presence in the UK "not conducive to the public good".
Defining what constitutes unacceptable activity merely makes public the extended criteria under which deportations will be considered.
But if certain individuals are arrested in the coming days and handed a deportation notice, there are almost bound to be legal challenges.
The chief obstacle for the government is likely to be the issue of torture.
The government's obligations under the UN Torture Convention and the European Human Rights Convention will not be diminished by the signing of memoranda of understanding with countries which have traditionally had a poor human rights record.
Thus, some foreign-born preachers and Islamic activists such as the Saudi, Muhammad al-Massari, and the Egyptian, Yasser al-Siri, are still likely to find protection in the courts if they face deportation to their countries of origin.
Even if the government follows through on its threat to amend the Human Rights Act, its objective of removing "preachers of hate" may still be thwarted.
'Glorify terrorism' offence
This makes it more likely that the Home Office will bring forward new legislation making it an offence to glorify terrorism.
Once that is on the statute book, there would be no obstacle to trying someone like Mr al-Massari in a criminal court.
Incitement to murder is, of course, already a criminal offence and incitement to commit a terrorist act abroad was made an offence under the Terrorism Act 2000. But the evidential threshold for both charges would be high.
Though the government has woken up rather late to the threat and influence of certain foreign-born Islamic radicals in the UK, it can be argued that so did the security service.
Even after 9/11, M15 was sanguine about the activities of high profile clerics such as Abu Qatada and Abu Hamza.
" We are less concerned with them than the people we don't know about" was the explanation offered.
In 2005, there is no such official complacency about the impact of extremist teaching on the young and impressionable.
But silencing it may still be hard to achieve.