'Nevertheless, the assault perpetrated by the defendant on the deceased - and an assault it was - was deliberate and, from the pathologist's report, was of considerable force,' he said.

'Regardless therefore that the activity was consensual, it must have been plain to him that what he was doing would place the deceased in considerable harm or even cause death.

'A deliberate doing of an act that puts the well-being or the life of another at risk, even with consent, must receive a sentence that reflects society's condemnation of such an activity,' he added.

It is believed to be the first case of its kind heard in a Hong Kong court.

Prosecutor Michael Arthur told the Court of First Instance that the prosecution accepted Yu's guilty plea to a charge of manslaughter despite the original charge of murder.

Mr Arthur told the court that on February 4 last year, the lovers had had sex and while they were lying in bed, Leung had teased her boyfriend of two years about his sexual ability and the size of his manhood - 'a sign for the sex game to take place'.

It was after this conversation that Yu told police he had grabbed his girlfriend's throat, first with his left hand and then with his right hand for about one minute.

When he discovered that she had not regained consciousness a few hours later, Yu contacted his friends. They heard the distraught man threatening to kill himself.

Mr Arthur said they turned to Yu's mother, who called police.

An examination of Yu and the deceased showed they both bore indications of asphyxia.