Police are looking into connections between far right-groups in the UK and the man responsible for killing 93 people in Norway, after David Cameron demanded security checks on extremists groups in Britain.
At a meeting of the National Security Council on Monday morning, the prime minister requested the checks following revelations that Anders Breivik may have met with British fascists.
In a "manifesto" the gunman published online shortly before the attacks, he mentioned far-right groups in the UK, including the English Defence League (EDL).
However the EDL have denied links with the Norwegian. In a statement the group said: "Brievik talks about the EDL in a negative light because of our anti-extremist stance".
"We can categorically state that there has never been any official contact between him and the EDL, our Facebook page had 100,000 supporters and receives tens of thousands of comments each day.
"And there is no evidence that Brievik was ever one of those 100,000 supporters. Even so, anyone who expresses any extremist beliefs of any kind, be it white supremacist, christian fundamentalist or Islamic extremists, they all get banned from the site."
The prime minister's official spokesman said on Monday morning: "We should ensure that we have adequate scrutiny of the behaviour of extremist individuals and groups."
A Metropolitan Police spokeswoman told the Huffington Post UK: "We are liaising with the Norwegian authorities".
Polish police are also probing links between Breivik and extremists in the country.