Thomas Mair, 52, made his defiant statement on Saturday in Westminster Magistrates’ Court in London.

West Yorkshire Police had charged Mair overnight with murder, inflicting grievous bodily harm, possession of a firearm with intent to commit a crime, and other gun charges, in the slaying on Thursday of 41-year-old Ms Cox. The killing brought Britain’s European Union referendum campaigning to a halt.

When the question about his name was repeated, Mair said the same words again, his only comments during the 15-minute hearing.

Wearing grey sports clothes and flanked by two security guards, Mair was charged with murder, causing grievous bodily harm, and possession of a firearm and another offensive weapon.

Mair was not required to enter a plea and his lawyer Keith Allen said there was no indication of what plea would be given.

Deputy chief magistrate Emma Arbuthnot ordered that he be remanded in custody until his next court appearance on Monday. The judge also suggested that a psychiatric report should be prepared.

“Bearing in mind the name he has just given, he ought to be seen by a psychiatrist,” she said.

A police van believed to be carrying Thomas Mair arrives at Westminster Magistrates’ Court.

Ms Cox was an advocate for keeping Britain inside the EU and had argued for better treatment of Syrian refugee children.

Evidence has emerged that the reclusive gardener suspected of slaying her had decades-old ties to a Neo-Nazi movement and an interest in anarchist weapons literature.

After detectives charged Mair with murder, authorities confirmed they were focused on his alleged links to white supremacists and history of mental illness as they sought a motive for an act of violence that has shocked Britain and brought normal political life to a halt.

Prime Minister David Cameron joined the stunned citizens of Birstall in paying tribute to their slain politician, Jo Cox, as they placed flowers and handwritten notes on a memorial and struggled to comprehend how one of their own could have so viciously killed her.

“Today our nation is rightly shocked,” Mr Cameron told a crowd that included witnesses to the killing and many of Ms Cox’s friends and colleagues, including MPs from both Mr Cameron’s ruling Conservative and Ms Cox’s opposition Labour Party. He urged the British people to drive intolerance and division “out of our public life and out of our communities.”

British Prime Minister David Cameron, centre, and Labour Party leader Jeremy Corbyn, right, arrive to lay flowers in memory of Jo Cox in Birstall. Pic: AFP

Metres away, police crime-scene tape blocked off street market stalls that just a day earlier were bustling with lunchtime trade as Ms Cox arrived outside the town’s library to field concerns from her constituents and see what she could do to fix them.

West Yorkshire’s police commander, Dee Collins, alleged Mr Mair attacked the 41-year-old MP as she emerged from her car alongside two aides. The attacker, she alleged, stabbed Ms Cox repeatedly with a hunting knife and shot her as she lay on the ground. He was arrested nearby.

Mr Mair is due to appear in a central London court later today (AEST).

“We have now charged a man with murder, grievous bodily harm, possession of a firearm with intent to commit an indictable offence and possession of an offensive weapon,” said Detective Superintendent Nick Wallen, who is leading the investigation.

Ms Collins said Mr Mair’s history of mental illness was “a clear line of inquiry” as were his alleged links to right-wing extremism and interest in Neo-Nazi materials. She said the regional counter-terrorism unit was aiding in the investigation, in part to determine any links with other extremists, but the Birstall native was believed to have acted alone.

Another question for detectives, she said, was how Mr Mair acquired a gun in a country that imposed a ban on handgun ownership following a 1996 school massacre in Scotland, in which a deranged gun club member killed 16 first graders and a teacher.

The Southern Poverty Law Centre, a US-based civil rights group that monitors hate groups, said Mr Mair had been a supporter of the National Alliance, “the most dangerous and violent Neo-Nazi group in the United States for decades.”

On its website, the centre published copies of receipts from 1999 to 2003 showing that Mr Mair ordered survivalist weapons guides and other extremist materials from the National Alliance. Among the publications were “Chemistry of Powder and Explosives” and “Improvised Munitions Handbook.” The address on the receipts corresponded to Mair’s address in a state housing project on the edge of Birstall, where two officers kept guard as detectives interviewed neighbours.

Few said they could believe the man they described as a reclusive gardener was capable of attacking anyone. The suspect’s brother, Scott Mair, told reporters his brother had a history of mental illness, but was not violent.

“When we saw his photo appear on the news as the suspect, me and my wife said, ‘Not in a million years,"’ said David Hallas, a neighbour of Mr Mair for more than a decade. “Of all the people in Birstall that I know, he would’ve been at the bottom of the list.”

Other online documentation linked Mair to a subscription to a pro-apartheid publication from South Africa, SA Patriot, and said he was one of its “earliest subscribers and supporters.”

Clarke Rothwell, a plumber who runs a cafe near the scene of the slaying, said the assailant shouted “Britain first!” several times as he shot and stabbed Ms Cox. An extreme right-wing group called Britain First denied any connection with Mr Mair.

Jo Cox addresses the House of Commons.

Ms Cox was a former aid worker who championed immigrant rights, bringing an end to Syria’s civil war and keeping the United Kingdom in the European Union. The day before her killing, Cox joined her husband and two young children in campaigning for the pro-EU cause on the River Thames, where the family had lived in a houseboat since her election last year.

British voters will be asked to decide whether to keep their country in the 28-nation bloc on Thursday. Anti-EU campaigners have argued that leaving the EU would allow Britain to curtail immigration. Both sides have suspended their campaigns through following Ms Cox’s killing, although some door-to-door leafleting was expected to resume sooner.

Labour Party leader Jeremy Corbyn, who joined Mr Cameron in Birstall, blamed Ms Cox’s death on “the well of hatred.” While the House of Commons had not been due to resume meeting until after the referendum, leaders agreed to a special recall on Monday to pay tribute to Ms Cox.

Police search near the crime scene in Birstall. Pic: AFP

As police combed the streets around the attack site, some mothers walking their children to a nearby school wiped away tears. Others quietly spoke of the brutality of the killing and its exceptionally public nature.

“I can’t get my head round the fact that Jo was attacked on the streets of Birstall in broad daylight, in public,” said Tina Walker, who worked alongside Ms Cox in promoting ethically sourced foods from developing nations — and who recalled how Ms Cox would hug anybody she recognised in town.

“I woke up this morning and just wanted to find it hadn’t happened. I was half expecting to see her here today, because that’s how your brain plays tricks on you,” she said.

Violence against British politicians has been rare since Northern Ireland’s peace deal nearly two decades ago. Ms Cox is the first serving politician to be killed since Conservative politician Ian Gow was killed by an Irish Republican Army bomb in 1990. While Parliament is protected by armed police, politicians spend much of their time in their home districts, generally without security. Since 2000, two politicians have been attacked and wounded while meeting constituents.

“We’ll be reviewing our security,” said Dan Jarvis, a Labour politician who represents Barnsley in the neighbouring South Yorkshire district, and is an army veteran who served in Iraq and Afghanistan.

“But I’ll walk through Barnsley today like every Friday,” he said.

With Jill Lawless

AP