A former altar boy has been jailed for 10 years for cutting the throat of a convicted paedophile after he confessed to sexually abusing a six-year-old child.

Christopher McMahon, 48, repeatedly stabbed his drinking partner, David Potter, 50, in the early hours of August 21 last year and left him face down on the floor of his flat in Tooting, south London.

Afterwards, the homeless defendant went to his on-off girlfriend's house, still soaked in his victim's blood, and told her: "I've done it."

Prosecutor Sarah Whitehouse QC had told jurors at the Old Bailey: "Mr McMahon said he had slit a man's throat and indeed he had."

Mr Potter was found dead in a pool of blood five days later after police were alerted by a concerned neighbour.

A post-mortem examination found he had stab wounds to his neck, the most severe of which had gone through to his spine and cut numerous blood vessels including his jugular vein.

The court heard that Mr Potter had pleaded guilty at Chester Crown Court in February 2000 to gross indecency with a child.

The charges related to two incidents of sexual abuse involving a girl in the late 1990s.

Giving evidence, McMahon said Mr Potter's drunken revelation had an immediate effect on him after he had suffered the effects of childhood abuse for 30 years.

The jury was told that McMahon had previously made allegations against a priest when he was an altar boy in the 1980s, but the matter was never reported to police.

Following a trial, McMahon was cleared of murder but was found guilty of manslaughter by reason of loss of control.

It can now be reported that the defendant was cleared in 2008 of the murder of Jill Grinstead, 63, who was beaten to death at her home in Wimbledon, south-west London.

As he appeared for sentencing, the court was told that his criminal career has spanned 30 years.

He has 46 previous convictions for 95 offences, mainly of theft and handling stolen goods to fund his addiction to drink and drugs.

In 2011 he was convicted of wounding a man in a pub by swinging a glass, causing a 1.5in (3.8cm) gash to his victim's head.

Judge Paul Dodgson QC accepted that McMahon had suffered abuse in his youth which may well have caused him "trauma" ever since.

But he told him: "Neither you nor those representing you have at any stage of this trial suggested Mr Potter deserves his fate.

"He was dealt at the time of this offence and no-one had any right either legally or morally to punish him again for that offence."