A Whitehall source told the publication that MI5 was reviewing the 74-page manifesto - they are also probing any links to far-right extremists in the UK.
Brenton Tarrant, a 28-year-old white supremacist obsessed with the Crusades, toured the Continent and came to Britain to stay for up to a fortnight in 2017.
Prime Minister Jacinda Ardern revealed that two other people were arrested in the incident and questioned about their involvement in the incident.
Ankara on Friday said it was investigating Tarrant's multiple visits to Turkey, and who he might have met while he was there.
He reportedly started to travel about 2011 after the death of his father, heading to Turkey and Pakistan, as well as the Balkans.
New Zealand security intelligence officers are also piecing together a picture of Tarrant's background that includes travelling the world and sporadically spending time in Dunedin.
MI5 has since launched the inquiry into any links between alleged perpetrators of the Christchurch mosque attacks and members of the United Kingdom far-right, according to The Times.
"This individual was not on the radar of either the New Zealand intelligence agencies to the Australian agencies".
The massacre is the deadliest attack in New Zealand's history.