A key part of Tony Blair's draconian anti-terrorism legislation was a clause barring the "encouragement" or "glorification" of terrorism. This being the UK, it was naturally written rather broadly, so that anyone who said that, in some circumstances, violent action against any government could be morally justified, or who praised or expressed approval of such action in the past (no matter how distant, and no matter how oppressive the government) would be liable to up to seven years imprisonment. The clause would have made it a crime to praise or support (among other things) the students of Tiananmen, the Prague Spring, the 1956 Hungarian Revolt, the massacred protestors of Andijan, the American Revolution, the UK's own "Glorious Revolution", and even the overthrow of Saddam Hussein (a kind of "premature anti-Ba'athism). In practice, the requirement for the Attorney-General to consent to prosecution meant that the law would be used only to target those whose expressed opinions or supported causes the government of the day did not like.
By criminalising such a broad range of expression, including mere abstract advocacy and historical argument, the clause would have been a gross attack on freedom of speech. Fortunately, it is no longer with us. The House of Lords - who once again seem to be the UK's last defenders of freedom - have voted overwhelmingly to dump it, setting up a showdown with the Commons. By constitutional convention, the Lords do not veto legislation from the government's election manifesto - and banning "glorification" was part of New Labour's 2005 election platform. But this is a case where the government is trying to abridge a fundamental freedom, and some of the peers seem to feel strongly enough about it to want to force the issue. That would most likely result in the Parliament Act being invoked, meaning that the bill would simply be delayed by one year and then become law - but that would require the government to restore the clause and then pass the bill in two separate sessions of Parliament over the course of a year, all of which requires a Parliamentary majority. Given that the "glorification" clause only passed the Commons by the skin of its teeth, that's not guaranteed, and a strong show of opposition from the Lords could sink it entirely.