The killer had spent the weeks leading up to the murder researching far-right extremists including the Nazis, the Ku Klux Klan and Norwegian mass killer Anders Breivik.

A far-right extremist was on Wednesday sentenced to life by a British court after he was found guilty of the “planned and pre-meditated murder” of Labour MP Jo Cox during the Brexit campaign.

Thomas Mair, who believed in white supremacy and had Nazi material stocked in his home, repeatedly shot and stabbed Cox during the EU referendum campaign.

Mair was convicted by a jury of murdering the 41-year-old Cox outside her West Yorkshire constituency surgery on June 16, a week before the UK’s referendum.

The 53-year-old, dressed in a dark suit and blue tie, remained impassive as the verdicts were read out, after an hour of deliberations on Wednesday.

The trial judge, Justice Wilkie, said the murder was carried out to “advance a political cause of violent white supremacism, associated with Nazism“.

“It is evident from your internet searches that your inspiration is not love of country, it is an admiration for Nazis and similar anti-democratic white supremacist creed,” he told Mair.

File photo of Britons paying floral tributes to Jo Cox, in Parliament Square, London, after the 41-year-old British MP was fatally injured in northern England. | Photo Credit: AP

The judge said he had concluded the offence was so exceptional that it has to be marked with a whole life sentence, which means Mair can only be released by an exceptional order by the UK’s home secretary.

The killer had spent the weeks leading up to the murder researching far-right extremists including the Nazis, the Ku Klux Klan and Norwegian mass killer Anders Breivik.

He also read material on the murder of MP Ian Gow by the Irish Republican Army in 1990 as part of compiling a dossier on Cox, a campaigner for the Remain camp in the EU referendum.

After the guilty verdict, Brendan Cox paid tribute to his wife and said the family had “no interest in the perpetrator.”

“We only feel pity for him... we are here because we want to tell you about Jo. What she was and what she meant to us,” he said.

Cox is also survived by her two young children, aged five and three.

Sue Hemming, head of special crime and counter terrorism at the Crown Prosecution Service said: “Mair has offered no explanation for his actions but the prosecution was able to demonstrate that, motivated by hate, his pre-meditated crimes were nothing less than acts of terrorism designed to advance his twisted ideology.”

Earlier, the murder trial had heard how Mair shouted “Britain first, this is for Britain” over Cox’s body after shooting her three times and inflicting 15 stab wounds.