A British judge on Wednesday sentenced Islamic State group follower Ali Harbi Ali to a whole-life prison term for murdering lawmaker David Amess in a knife attack last year.

"This is a murder that struck at the heart of democracy," judge Nigel Sweeney said as he handed down his sentence at London's Old Bailey courthouse, noting the 26-year-old defendant had shown "no remorse or shame".

Sweeney added he had no doubt it was an "exceptional case" that merited the sentence, which comes two days after a London jury unanimously found Ali guilty of the ferocious knife attack last October.

It was the second murder of a British MP in five years and prompted calls for better security for elected representatives.

Ali, who pursed his lips briefly as the judge handed down his sentence, had told the trial that he had no regrets about killing father-of-five Amess in revenge for votes in parliament for air strikes in Syria in 2014 and 2015.

He stabbed Amess more than 20 times with a foot-long carving knife as he met constituents in a church in Leigh-on-Sea, southeast England, before being apprehended at the scene of the murder.

In a statement following the sentencing, Amess' family said it provided "no elation" and that nothing could ever compensate for the "appalling and violent manner" in which he was murdered.

"We will struggle through each day for the rest of our lives," it noted.

"It breaks our heart to know that our husband and father would have greeted the murderer with a smile of friendship and would have been anxious to help. How sickening to think what happened next. It is beyond evil."