A right wing nationalist repeatedly said "Britain First" as he shot Labour MP Jo Cox three times and stabbed her in the street, the Old Bailey heard.

Thomas Mair, 53, ambushed the mother-of-two as she arrived for a regular surgery with her Batley and Spen constituents in June this year.

Prosecutor Richard Whittam QC told jurors Mair had planned the attack in advance and carried out the murder because of his "strong political and ideological interests".

Jurors at the Old Bailey were told Mair had researched the Ku Klux Klan, Nazis, serial killers and right wing politicians in the days prior to killing Ms Cox.

He had also used his local library to research Ms Cox, fellow Yorkshire MP William Hague, and Ian Gow, an MP murdered by the Provisional IRA.

"She was brutally murdered by one of her constituents, this defendant, Thomas Mair", said the prosecution.

"It was a cowardly attack by a man armed with a firearm and a knife.

"Jo Cox was shot three times and suffered multiple stab wounds.

"During the course of the murder Thomas Mair was heard by a number of witnesses to say repeatedly ‘Britain First’."

During the attack, a pensioner, 77-year-old Bernard Kenny, tried to save the 40-year-old MP and was also stabbed by Mair, it is said.

Mr Whittam said the shocking attack, on June 16 in Birstall, West Yorkshire, came just a week before the EU referendum.

He said Ms Cox had been a vocal Remain campaigner, having first been elected as an MP a year earlier, and had spoken in Parliament of "her joy at representing a diverse community".

Ms Cox was attacked just before 1pm as she arrived in Market Street, Birstall, for a planned surgery meeting.

"The murder took place whilst she was performing her role as a Member of Parliament", said Mr Whittam.

"Thomas Mair’s intention was to kill her in what was a planned and pre-meditated murder for a political and/or ideological cause.

"The firearm used was a .22 weapon that had been adapted to be used as a weapon to kill. He also used a dagger-like knife."

Paramedics tried to save the MP's life but she died less than an hour later.

Mair, of Lowood Lane in Birstall, denies murder, causing grievous bodily harm, possession of a firearm with intent to commit an indictable offence and possession of an offensive weapon.

The trial continues.