By Michael Holden and Guy Faulconbridge

LONDON (Reuters) - The man charged with murdering British lawmaker Jo Cox gave his name as "death to traitors, freedom for Britain" when he appeared in court on Saturday accused of a killing that could be a defining moment in a vote on European Union membership.

The murder of Cox, a 41-year-old mother of two young children, has shocked Britain, elicited condolences from leaders around the world and raised questions about the tone of campaigning before the EU referendum which takes place next Thursday.

Cox, an ardent supporter of EU membership, was shot and stabbed in the street in her electoral district in northern England on Thursday.

Wearing a gray sweat shirt and trousers and flanked by two security guards, 52-year-old Thomas Mair was asked his name by a clerk at Westminster Magistrates' Court in London.

"Death to traitors, freedom for Britain," Mair said. When asked again what his name was, Mair calmly repeated: "My name is death to traitors, freedom for Britain."

"Bearing in mind the name he has just given, he ought to be seen by a psychiatrist," Deputy Chief Magistrate Emma Arbuthnot told the court.

Mair, balding with a gray goatee beard, made no further comment in the 15-minute hearing, his first appearance in public since police arrested him in the town of Birstall, Yorkshire, where Cox was killed.

His brief comment in court furthered suggestions that the attack was politically-motivated as it echoed the message put forward by those supporting a so-called Brexit that leaving the EU would be a vote for freedom.

The case is also being by handled by the counter-terrorism unit of Britain's Crown Prosecution Service.

Prosecutor David Cawthorne told the court that those who witnessed the attack said Cox had been repeatedly stabbed and then shot three times as she lay on the ground.

Her attacker was heard saying "Britain first, Keep Britain independent, Britain always comes first," Cawthorne said. When he was arrested by police he told them "I'm a political activist", the prosecutor told the court.

Material relating to far right ideology was found in a search of his home, Cawthorne said.

Mair is charged with murder, causing grievous bodily harm, and possession of a firearm and a knife. He was remanded in custody and will appear at London's Old Bailey court on Monday.

The killing has shocked the nation. Both sides have temporarily suspended campaigning ahead of Thursday's vote, which has far reaching implications for both the EU and Britain.

A British exit from the EU would rock the bloc - already shaken by differences over migration and the future of the euro zone - by ripping away its second-largest economy, one of its top two military powers and by far its richest financial center.

Pro-Europeans, including former prime ministers Tony Blair and John Major, have warned that an exit could also trigger the break-up of the United Kingdom by prompting another Scottish independence vote if England pulled Scotland out of the EU.


Prime Minister David Cameron joined Labour leader Jeremy Corbyn on Friday to lay flowers in Birstall.

"It is a vile act that has killed her," Corbyn said.

Cameron has agreed to recall parliament on Monday to allow lawmakers to pay tributes to the popular Member of Parliament (MP), who was only elected in 2015.

The murder has sparked debate in Britain, which has strict gun controls, about the safety of lawmakers, the heightened tempo of political confrontation and any impact on the EU vote.

Both sides in the referendum contest have put on hold their national campaigns until at least Sunday.

Polls have suggested the vote hangs in the balance, but in the last week a series of surveys have indicated that the campaign to leave had been taking the lead.

A telephone survey by BMG for Scotland's The Herald newspaper on Saturday showed the "In" camp on 53 percent and "Out" on 47 percent, although a separate online poll by BMG showed Out leading by 10 points, with 55 percent support compared to In's 45 percent.

Both polls were carried out before the killing of Cox.

Those wanting to stay in the EU can count on the support of many of Britain's biggest businesses, most economists and foreign leaders such as U.S. President Barack Obama, who spoke to Cox's husband on Friday to offer condolences.

The International Monetary Fund, which has previously warned that Britain and the world economy could be hit by a so-called Brexit, said on Saturday an exit could leave Britain's economy more than 5 percent smaller by 2019.

However, the "Out" campaign's message that EU membership is responsible for a loss of political control as well as uncontrolled immigration appears to have struck a chord.

Members of the 'Out' campaign say Britain would prosper if it broke free from what they say is a doomed German-dominated bloc that punches way below its weight beside rivals such as Russian President Vladimir Putin.

Both sides have accused each other of making up facts to support their case, and debates had become more heated and personal in the days before Cox's death, with London Mayor Sadiq Khan telling Sky News politics had become "poisonous".

"The referendum was always about more than Europe; it was always about what kind of Britain we are and what we aspire to be," former Prime Minister Gordon Brown wrote in Saturday's Guardian newspaper.

"But some have attempted to hijack a decision on the future of Britain in Europe and turn it into a vote on immigration, and then on immigrants and those who support immigrants."


Cox had arrived in Birstall for an advice session with constituents in a public library.

Bernard Carter-Kenny, a 77-year-old who had taken his wife to the library, intervened to try to protect Cox after she was attacked and is in hospital after being stabbed in the stomach.

Armed police patrol Westminster, where lawmakers do much of their work in parliament, but there is often no security in their home electoral districts, or constituencies.

The last British lawmaker to have been killed was Ian Gow, who died after an Irish Republican Army (IRA) bomb exploded under his car at his home in 1990.

The Daily Telegraph newspaper reported that women MPs had repeatedly raised concerns about their security with Cameron's office, with one writing to say if it was not improved there would be a "tragic fatality".

Police have said they had reiterated advice and guidance to MPs, some of whom have canceled surgeries after the killing of Cox, a former charity worker whose job took her to countries such as Afghanistan and Darfur.

In Birstall, hundreds of bouquets of flowers were laid in the town center with locals still stunned by what had happened.

"Over the last few weeks the debate about Europe has not been what it should be," local vicar Paul Knight told Reuters.

"We all recognize the exaggerations, hyperbole, and anger. And unless that changes, and we've only got a few days for that to change, then it's very sad.

"I hope people reflecting on this will realize democracy actually means speaking, and not violence and not anger."

(Additional reporting by Paul Sandle; Writing by Guy Faulconbridge; Editing by Richard Balmforth)