Marine Le Pen, the French far-right leader, has joined anti-immigration politicians in linking the London attack to migrant policy, despite the attacker being British.

Le Pen, who is forecast to reach the second round runoff in France’s presidential election in May, said on Thursday the attack underlined the importance of countries being able to protect their borders and stepping up general security measures.

“We must control our borders,” the Front National leader told France’s BFM TV and RMC radio. “The problem we have today is this form of low-cost terrorism, radicalised individuals acting alone, without a network. It’s a new form of terrorism that requires all the measures we are not taking at present.”

The attack has made headlines across Europe but particularly in France, after the Paris and Nice attacks of 2015 and 2016 respectively claimed nearly 230 lives, and where the country is still under a state of emergency and themes of security and immigration are dominating the election campaign.

Poland’s prime minister, Beata Szydło, also drew a link between the attack and the EU’s migrant policy, saying it vindicated Warsaw’s refusal to take in refugees under the EU’s quota scheme.

“I hear in Europe very often: do not connect the migration policy with terrorism, but it is impossible not to connect them,” Szydło told private Polish broadcaster TVN24.

She added that the EU’s migration commissioner, Dimitris Avramopoulos, on a visit to Warsaw, was “trying to tell us: you have to take these migrants … And two days later another terrorist attack in London occurs”.

Theresa May said on Thursday the attacker – who killed three people and injured 29, including seven critically, before being shot dead by police – was British-born and had been investigated “some years ago” by MI5 in relation to concerns about violent extremism.

The Ukip donor Arron Banks drew a similar link, tweeting on Wednesday: “Teresa [sic] May was Home Secretary for 6 year when over a million illegals were allowed into our country. I don’t think I’ve ever felt more sick.”

Teresa May was Home Secretary for 6 year when over a million illegals were allowed into our country. I don't think I've ever felt more sick. https://t.co/K9wMxQfb3f — Arron Banks (@Arron_banks) March 22, 2017

Leave.EU accused mainstream politicians of “facilitating acts of terror almost identical to this throughout western Europe in recent times”.

May had “failed to implement the British people’s desire to have secure borders and … has overseen unprecedented levels of immigration”, the campaign group said.

It later tweeted: “British-born means nothing if he lived in a segregated community and hated the British way of life … Not British at all,” and: “Government inaction to address segregation in our society facilitates these acts of terror.”

Government inaction to address segregation in our society facilitates these acts of terror. When will Establishment groups like you wake up? https://t.co/yAwqaSZk9Y — LEAVE.EU (@LeaveEUOfficial) March 23, 2017

The former Ukip leader Nigel Farage appeared twice on US television on Thursday, arguing that the London attacks proved Donald Trump’s hardline immigration and anti-Muslim policies were correct.

“Surely this is the big takeout: when Donald Trump tries to makes America safer, when Donald Trump tries to make sure that these scenes we’ve had in Paris, Brussels and Berlin and now London aren’t repeated in America, we have people on Fifth Avenue and behind me in Westminster out on the streets protesting. It seems to me our political leaders really ought to start saying sorry,” he told Tucker Carlson on Fox News on Thursday morning.



He later argued that lawmakers who encouraged open immigration were responsible for the attacks. “What these politicians have done for the last 15 years may well affect how we live in this country for the next 100 years,” he said.



He was not the only hardline conservative to appear in the US media. The Daily Mail columnist Katie Hopkins also appeared on Carlson’s Fox show, echoing Farage’s xenophobic rhetoric.



“We’re a country that spends so much time tiptoeing around the cultures that refuse to join us and not enough time defending the culture they have chosen to join, but because I say those things I am widely hated for those views,” she said. “People are cowed, people are afraid and people are not united.”



British writers on US “alt-right” websites used the attack to incite hatred against Muslims. In a video on InfoWars, a site that published conspiracy theories about Hillary Clinton’s health during the 2016 election, Paul Joseph Watson argued that it was time to “acknowledge that Islam is not a religion of peace and in serious need of reform”.



On Breitbart News, whose former executive chair Steve Bannon is now one of Trump’s most influential advisers, James Delingpole, the executive editor of its UK section, wrote a column declaring that Islamic terror attacks could end western liberal values.

