Unlike Facebook, Twitter also decline to monitor postings systematically, relying on other users or government officials to report breaches of its terms of use. All this leaves a lot of wiggle-room for Isil members to post without being blocked.
This is where Theresa May's proposed proposed new orders come in - effectively giving the authorities the right to censor postings by those extremists who are subject to them.
The new orders could prevent British-based Twitter users from tweeting their support for groups such as Isil.
British supporters of the group, including are now fighting in Iraq and Syria, have used Twitter to appeal for new members and to threaten the British state.
In July, a Twitter user believed to be Nasser Muthana, 20, from Cardiff now thought to be in Syria, posted a picture of a stack improvised explosive devices in a garage. He tweeted: "So the UK is afraid I come back with the skills I've gained."
Muthana, a former medical student, had earlier appeared in an Isil recruitment video which was widely circulated on the internet.
Privately-educated Aqsa Mahmood, 20, from Glasgow, has also travelled to the Middle East and has allegedly encouraged terrorist acts via a Twitter account under the name Umm Layth.
Both accounts have since been deleted.