Far-right activists have launched a campaign of intimidation and violence against political opponents including a series of death threats and physical attacks.

Hardline fascists are targeting students and leading anti-racism activists who campaigned against the British National party in June's European elections.

A group calling itself the Aryan Martyrs' Brigade has issued threats including a "death warrant" sent to Weyman Bennett, the joint secretary of Unite Against Fascism, stating he will be killed before the end of the year "for crimes against all loyal white patriots and British nationalists".

The threat, which the police are investigating and has a picture of Bennett in cross hairs, states: "We know exactly what you look like and what venues you frequent and can strike at will. The police, special branch, MI5, Searchlight cannot save you from the bullets coming your way. No matter where you are, we will get you, all we need is a lock on your mobile phone signal and you are one dead nigger."

Others have received threatening emails and at least one prominent activist was attacked after his picture appeared on an extreme rightwing website that was taken during protests against the BNP.

"There has definitely been an upsurge in attacks and intimidation since the European elections," said Bennett. "The fringe rightwing groups appeared to be on their best behaviour when the BNP were campaigning but once the election was over they seem to be trying to take their revenge on those of us who were prominent in the anti-fascist campaign."

The increase in rightwing violence comes after Scotland Yard admitted it was deploying more resources to monitor far-right extremists amid fears of a terrorist attack. Commander Shaun Sawyer told a meeting organised by the Muslim Safety Forum last month that there was a growing threat from the far right.

"I fear they will have a spectacular …they will carry out an attack that will lead to a loss of life or injury to a community somewhere," he said.

Sawyer added that more specialist officers needed to be deployed to counter the threat from far-right groups.

Bennett, who has received threats in the past, has been told by the police to take the latest death threat more seriously.

"Standing up against people like the BNP you do sometimes get verbal threats and intimidation but this appears to be more serious," he said. "I don't intend to stop organising anti-racism events or confronting the fascists in the BNP but something like this does make me think more about my personal security."

One of the people who has been assaulted in recent weeks is Gary McNally, who helped organise a Love Music Hate Racism festival in Stoke-on-Trent in May. After the European elections, when the BNP gained two MEPs, the 23-year-old attended a protest outside a meeting in Blackpool. Several photographs of the student appeared on the extremist Redwatch website, which is understood to be linked to the Aryan Martyrs' Brigade, alongside the slogan "Remember places, traitors' faces, they'll all pay for their crimes". A few days later McNally was attacked.

"I was about 200 yards from my house and I felt something smash against my face and I heard the words, 'You are a disgrace to your country,' and I saw a pair of shoes as I fell to the ground," he said.

McNally, a student at Staffordshire University, was taken to hospital where he was treated for cuts and bruises to his face and head.

"After I had been hit I thought I had gone blind in my left eye. The attack has left me very scared – the BNP put on this respectable front but I suppose this is the reality of what happens if you publicly stand up and disagree with them."

Simon Darby, deputy leader of the BNP, said the attacks and threats had nothing to do with the party.

"It is rather ironic that they are complaining about being attacked when they use similar tactics themselves," he added.