Damian Collins, the chairman of the UK Commons culture committee, said it appeared to be a "terror attack designed for social media" and demonstrated why there had to be "statutory regulation of the distribution of content online through social networks".
"It's a viral contagion spread through social media, helped by their algorithms. The firms need to carry out a major audit into who was sharing this film and how it was shared. Groups have deliberately spread it and those accounts should be closed down."
Tarrant, 28, from Grafton, Australia, appeared in court today charged with murder. He was detained in custody without plea.
The Facebook video of the killings was viewed 23,000 times in an hour and was only taken down after 239,924 people had watched it.
But 10 hours after the attack the footage was still being shared on YouTube, despite complaints.
Tom Watson, Labour's deputy leader, said the response was "not good enough" after YouTube, owned by Google, "reviewed" a copy of the video before removing it.
Facebook said it acted quickly to delete the video after being alerted by police. YouTube said it was "working vigilantly to remove violent footage."
And a Twitter spokesman said it had "rigorous processes and a dedicated team" for such emergencies.
Theresa May said the Government expected tech companies to "act more quickly to remove terrorist content".
Her spokesman said: "There should be no safe spaces for terrorists to promote and share their extreme views and radicalise others."
In a televised message, May sent New Zealand Britain's "deepest condolences" adding that targeting people at their place of worship was "despicable".
She said: "There can be no place in our societies for the vile ideology that drives and incites hatred and fear."
Jacinda Ardern, the New Zealand prime minister, described the attacks as "one of New Zealand's darkest days".
In the UK, police stepped up patrols around mosques for Friday prayers.
- The Daily Telegraph
