ISIS in Britain

The Telegraph reports that

The Prime Minister warned that the current crisis in Iraq must not be dismissed as a foreign problem because the same terrorists are planning to “attack us here at home in the United Kingdom”. 

Unfortunately,  other than drawing the public's attention to the problem, he gives no indication as to what the government is proposing to do about the problem.
His reported responses, at Question Time in Parliament, cast no light on what steps, if any, the government is proposing to take, other than telling us that:
British born extremists fighting in Iraq and Syria now represent the most serious threat to our security.

This, and his other answers, when examined closely, amount to little more than meaningless waffle. Clearly he believes that having drawn attention to the problem he has done his duty and the problem will go away. He tells us that:
The right answer is to be long term, hard-headed, patient and intelligent with the interventions that we make, and the most important intervention of all is to make sure that these governments are fully representative of the people who live in their countries, that they close down the ungoverned space, and they remove the support for the extremists.

What on earth has that got to do with the threat that within this country caused by returning extremists?

The United States has laws by which they can ban people from visiting proscribed countries without specific permission. Of course this does not stop anyone going to these countries, but if, on returning, there is evidence that they have been to such countries, they can be charged with a criminal offence and imprisoned if found guilty.

Surely, as a minimum, we could do the same. Were the government to declare ISIS as an enemy of this country, one would have thought that any British Citizens consorting with them would be guilty of treason, and here my only regret is that the Blair government removed the death penalty for treason.
Additionally, it would appear that many of those going to the Middle East from this country are not British Citizens, but "refugees" or "asylum seekers" with "leave to remain". This "leave" can be withdrawn and the Home Office should make it clear that this will be done in the case of anyone who visits the Middle East. If they willingly return to the countries from which they came, they are hardly refugees!

Cameron has admitted that extremists present a grave danger to this country, now he has to show that he is taking real action rather than talking about the problem.