The threat from the rise of far-right terrorism in Britain could be diminishing after Boris Johnson’s election victory because supporters of the ideology feel they are being listened to, according to a former head of MI5.

Lord Evans of Weardale said “alienated” voters normally vulnerable to exploitation by far-right groups such as the British National party (BNP), English Defence League (EDL) and National Action might feel that their voices had been heard at the ballot box with the significant win for the Conservatives in December’s election.

The former MI5 director general, who led Britain’s domestic security service between 2006 and 2013, said: “Whatever you think of the outcome of the recent election in the UK, the fact that some of the legitimate concerns that were being used as a pretext by English nationalists have now been formally acknowledged at the ballot box might be a good outcome, even though it is sort of disconcerting for southern liberals.

“There was a significant alienated and disenfranchised group out there who didn’t think the system was taking any notice of them. And that’s where you need to be concerned about extremists exploiting legitimate concerns.

“Disaffected English nationalists were manifesting themselves at the extremes in things like the British National party and National Action, which fed the undertone that articulated itself as extreme rightwing terrorism.”

However, the crossbench peer warned that it remained to be seen whether potential far-right supporters would be wholly satisfied by Johnson’s administration.

“Attention still needs to be paid to this group, as it is not clear that they will feel entirely assuaged as a result of the fact that people are paying wider attention to them now. Terrorist problems emerge when you have a significant population who feel alienated and nobody takes notice of them, causing frustration and anger,” he added.

Evans, who was made a life peer in 2014, made the comments in an interview with the US-based Combat Terrorism Center. He has previously said the rise of far-right terrorism in Britain has been encouraged by years of austerity following the 2008 recession.

“I suspect it is a reflection of the social pressures on communities as a result of austerity measures. There seems to be a constituency of disaffected males (for the most part, but not entirely) who find extreme rightwing beliefs attractive. And they have started to get their acts together to organise into groups and plot.”

In the interview, he said some far-right terrorists had been “consciously and deliberately inspired by the perceived success of violent Islamists”.

He added that the EDL was “mutually symbiotic” with Anjem Choudary’s al-Muhajiroun group and described the emergence of neo-Nazi terrorist organisation National Action and its successor groups, which have described their ideology as “white jihad”, as predictable.

He added: “There is some evidence that they have been consciously and deliberately inspired by the perceived success of the violent Islamists in getting their grievances on the table as a result of violence and thought, ‘Well, we can do something like that.’”

Last September the head of counterterror police, Neil Basu, vowed to thwart the rise of the far right, which the force has said is the fastest-growing terrorist threat in the UK.

The number of white terror suspects being arrested in the UK has outstripped those of Asian background for two years in a row, and of the 25 attack plots that have been foiled since March 2017, 16 were Islamist, eight far right and one “other”.

In 2018 MI5 took the lead in investigating the most dangerous extreme rightwing terrorists in a sign of how seriously the threat was being taken.

Some terrorists were incited by extreme rightwing propaganda, such as Thomas Mair, who murdered the MP Jo Cox in 2016. But others, like Darren Osborne, who attacked Muslim worshippers with a van in north London, had acted after reading lawful material from groups such as the EDL and mainstream media.