The anonymous expert on right-wing extremism warned that the Government is putting an emphasis on the “global jihadist agenda” while possibly ignoring the growth of the far-right at home.
The adviser warned about the prospect of a violent attack being carried out by the far-right in Britain that could have been stopped.
He told BBC Radio 4’s Today programme: “I have been working with people from the far-right for about 27 years now, I can see increases in some of these groups and membership in some of these groups based on things that are happening nationally here and internationally.
“A lot of the emphasis is put on the global jihadist agenda, which is fine, and it needs to be, but I really feel that this agenda, the repercussions of some of that in terms of the far-right can’t be ignored.
“I wouldn’t want to get to the point where something happens and we look back and think actually we should have addressed that as well.”
The expert said he had met someone who wanted to put everyone who was not white British into Nazi-style death camps.
He told the programme: “I had one person who said he would like to implement death camps here in the UK and when I asked who he would like to put in the death camps, he just listed everyone that he didn’t see as white British.
“So that was every Asian person, every black person.”
Labour former communities secretary Hazel Blears said the Government needs to better support the Muslim majority who condemn Islamist extremism.
She called on ministers to beef up the anti-extremism Prevent programme and bring different communities together.
Efforts should be made to work with more young Muslims and encourage people from the community to become school governors and magistrates, she added.
Ms Blears said: “I honestly do not think that the Government is doing enough in the whole Prevent programme to bring people together and to support the Muslim majority who are absolutely horrified at what’s been happening.”