Police said on Saturday they have charged a 52-year-old man with the murder of British MP Jo Cox following an attack that has brought campaigning for next week's referendum on European Union membership to a standstill.

Thomas Mair is charged with killing Cox, 41, a member of the Labour Party and supporter of Britain staying in the EU, who was shot and stabbed to death in the street in her own constituency in northern England on Thursday.

Cox was targeted in the attack as she prepared to hold a regular session to give advice to constituents.

A 77-year-old man who intervened to try to protect Cox remains in hospital in a stable condition after suffering a serious injury to his abdomen.

Mair, who lives in the town of Birstall, in Yorkshire, where Cox was slain, will appear at London's Westminster Magistrates on Saturday charged with murder, causing grievous bodily harm and offences related to possession of a firearm.

Cox' killing has shocked the nation, uniting politicians in horror and leading to the suspension of hostilities in what had become increasingly bitter and ugly campaigning ahead of the June 23 referendum on the EU.

On Friday, Prime Minister David Cameron joined Labour leader Jeremy Corbyn in laying flowers in Birstall.

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

Cameron has agreed to recall parliament on Monday to allow MPs pay tributes to Cox who had only been elected to parliament in 2015.

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

Polls have suggested the vote is on a knife edge but in the last week had indicated that the campaign to leave the EU had been taking the lead.

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

Attacks of any nature on public figures in Britain are rare. The last British lawmaker to have been killed was Ian Gow, who died after a bomb planted by the Irish Republican Army (IRA) exploded under his car at his home in southern England in 1990.

Cox had arrived in Birstall for a "surgery" in a library with members of the public, a one-to-one meeting much like when a patient consults a doctor.

In Westminster, where lawmakers do much of their work in parliament, armed police patrol the entrances, corridors and halls but there is often no security in their own constituencies.

Leaders across Europe and the world have expressed shock at the killing of Cox, a Cambridge University graduate and former charity worker whose job took her to countries such as Afghanistan and Darfur.

A fund set up in her honour had raised more than 140,000 pounds for charities she supported in six hours.