In the wake of the London bombings, Tony Blair promised "tough" action from his government, including deporting those accused of supporting terrorism to countries where they faced a substantial risk of persecution and torture. His government has now formalised this plan, and announced that it will move "very quickly" to start deportations.
There are two problems with this. The first is that it is grossly contrary to the UK's obligations under the UN Convention Against Torture, which prohibits expelling or deporting someone where there are "substantial grounds for believing" that they would be tortured. While the British government has sought assurances from potential host governments that anyone they deport would not be subjected to such treatment, these are not worth the paper they're written on, and the UN HRC's special rapporteur on torture has already declared that such expulsions would violate the convention. If the person is a refugee, then they would also be covered under anti-refoulement provision in the Refugee Convention. And then there's British law... the UK's Human Rights Act implements the ECHR's provision barring torture, and any deportation could easily be challenged under this.
The second problem is that the criteria include "writing, producing, publishing or distributing material, public speaking including preaching, running a website; or using a position of responsibility" to express views which "justify or glorify terrorist violence". Note not specifically inciting crimes or even advocating that such attacks occur, but simply saying they are morally justifiable. No matter which way you slice it, this is a fundamental attack on freedom of speech. It will be challenged in court, and it is difficult to imagine the court which freed the Belmarsh detainees on the basis that indefinite detention for immigrants but not citizens was blatantly discriminatory upholding similarly discriminatory restrictions on speech. I'll also add that I can think of no better way to alienate moderate Muslisms than to enshrine a double standard which punishes those who defend terrorist violence against civilians, while those who defend US or Israeli violence against civilians suffer no penalty. You don't win a war of ideas through censorship, and you don't win it by that sort of public hypocrisy either.