I know it's against the law to be a member of a terrorist organisation but is it against the law to say that you support their ideals, their movement and their actions? Is it against the law to own content produced by a terrorist organisation like photos, music or videos?
I believe so. When the video showing the murder of Stuart Foley was released I believe the government released a statement reminding people that it was a crime to watch it or to share it on social media as it would be seen as propagating terrorism.
No. In NI you can openly express support for Sinn Fein and the IRA. Indeed you can endorse them officially by voting for their candidates and putting them in government.
"It seems that the writing of a book, an article or a blog, may therefore amount to terrorism if publication is for the purpose of advancing a political, religious, racial or ideological cause, designed to influence the government and liable to endanger life, or create a serious risk to health or safety."