Neil Hannah ... died after being hit outside a London pub.

Neil Hannah ... died after being hit outside a London pub.

A boxer who king hit and killed an Australian-born man living in London has been sentenced to seven years' jail.

Graham Brett, 50, was under the influence of alcohol and cocaine when he punched Neil Hannah, 49, outside a Pimlico pub in August 2012.

Mr Hannah, who came to the United Kingdom as a young man, was described in court on Monday as a "friendly gentle giant".

Brett, an ex-professional boxer who now coaches amateurs, pleaded guilty to manslaughter after previously denying murder.

The Australian-born victim died on August 7, five days after being hit so hard he instantly collapsed to the ground.

His skull was fractured in two places as it slammed into the pavement.

Justice Jeremy Stuart-Smith accepted Brett didn't intend to kill Mr Hannah.

"But hitting an unfit and overweight 49-year-old carried a foreseeable risk that he would fall and hurt himself," Justice Stuart-Smith said in sentencing Brett.

"It was unprovoked and completely unjustified even if Mr Hannah did, as you say, call you a Pommy ct."

When arrested Brett told police: "The geezer went to bite my nose off. I hit him and he went down."

But extensive CCTV footage shown in court on Monday proved much of Brett's initial account was untrue.

The victim could not have bitten Brett as he'd removed his top dentures.

Prosector Gillian Etherton QC told the Old Bailey that Mr Hannah's "in your face" humour and friendliness could sometimes irritate people.

But she argued, and Justice Stuart-Smith agreed, there was nothing aggressive in his manner.

Brett beckoned Mr Hannah outside The Greyhound pub after only a brief interaction inside.

He took his glasses off en route before punching Mr Hannah in the jaw.

He then put his glasses back on and returned to the pub.

The former railway worker smoked a cigarette and drank a pint before leaving The Greyhound.

Defence lawyer Gareth Morley said Brett had earlier warned Mr Hannah: "Don't talk to me like that - fk off from here or there could be trouble".

Mr Morley said his client was "much more sinner than saint" but noted he was "emaciated" by the ravages of alcohol addiction.

Justice Stuart-Smith sentenced Brett to seven years jail saying the public needed to be protected from his gratuitous violence.

Half that sentence can be served in the community.

Brett had previously been jailed for violent attacks and was banned from numerous pubs and clubs in London.

AAP