LONDON — In the shadows of Big Ben, in a building right next door to the Prime Minister's residence at 10 Downing Street, a non-descript concrete structure houses a court that few Brits know exist, let alone Americans.

Josephine McMillen of Middlebury, Conn., began learning all about the special court soon after her daughter's convicted killer, William Labrador, appealed his May 2001 conviction and life sentence in a court in the capital of the British Virgin Islands.

McMillen arrived at the Judicial Committee of the Privy Council on Monday morning dressed from hat to shoes in black, as she had throughout Labrador's six-week trial on the island of Tortola. McMillen made the trans-Atlantic journey against doctor's orders so that she could listen to Labrador's complaints to the five-member court — which serves as a sort of Supreme Court for cases arising from dependent territories of the Caribbean — about the way his conviction was attained.

``I think it is so important for me to be here to represent my daughter. That's why I'm here,'' McMillen said Monday during a break in what is expected to be a three-day hearing.

Lois McMillen, a 34-year-old artist from an affluent family, was found battered and drowned on January 15, 2000, a few miles from her family's vacation villa.

For her convicted killer, a 39-year-old former modeling company executive from New York, the council is his last hope for a court ruling that could either quash his conviction altogether or at least offer him the chance of a new trial.

The Judicial Committee of the Privy Council conducts its business in a cavernous chamber that is a perfect square with 50-foot tall walls. Observers sit in well-worn red leather chairs. In all it is an unlikely setting for a case that began on a perfect sunny day on a tropical island more than three years ago.

Shortly after McMillen's body was found on the rocky shores of Tortola investigators quickly focused on Americans Labrador and his three vacationing friends — Alexander Benedetto, Michael Spicer and Evan George. After being held for more than 15 months on suspicion they helped Labrador cover up the murder, the trial judge cited a lack of evidence and directed jurors to acquit the three friends without hearing their defense.

A prison informant then testified that Labrador admitted to drowning McMillen after an argument over money.

Labrador's basic complaint is that he was jailed on mere suspicion and convicted based solely on the testimony of a convicted swindler with a history of telling authorities his cellmates confessed murder.

Defense lawyers also claim the trial judge and prosecutors denied the defense a full opportunity to tell jurors about the inmate's many motives for lying about the case. They argue that the jailhouse snitch — convicted Texas con man Jeffrey Plante — got much of his information by reading media accounts McMillen's drowning death.

Labrador was not allowed to attend the proceedings in London and instead remains tending to his small garden at Her Majesty's Prison on Tortola, a dot of an island east of Puerto Rico. Labrador is being represented for his appeal by barrister Edward Fitzgerald, who holds the distinguished title of Queen's Counsel. Wearing a black robe and white, pony-tailed wig that all lawyers must wear when arguing before the panel, Fitzgerald argued Labrador's case for nearly four hours Monday.

Fitzgerald stressed that no "safe verdict'' could come based solely word on Plante.

``That was not a fair trial,'' said Fitzgerald, who agreed to handle Labrador's appeal for free after a friend of Labrador's sent him a long letter urging him to take the case.

Fitzgerald has had success before the council before with a similar argument. Recently the committee threw out a murder conviction in Jamaica. Although there was significant evidence of motive, the committee ruled that the trial judge committed reversible error by failing to caution jurors that an inmate who testified the defendant confessed could have been trying to "ingratiate" himself with authorities.

When Labrador's cellmate, Plante, approached authorities in May 2000, the case against Labrador was about to go to a magistrate for a determination of whether enough evidence existed to warrant a trial. Plante, whose extradition was being sought by Texas, turned out to be the only direct evidence at that hearing and the subsequent trial.

Plante's story was that Labrador "got religious" as Easter approached a few months after McMillen's death and Labrador confessed that he killed her because she was "no good" and they argued about money.

At Monday's hearing Fitzgerald stressed the committee's recent ruling about the duty of judges to caution juries about such inmate testimony.  "It is an obligation, not a discretion,'' Fitzgerald said. "Whenever there is a reason to doubt the reliability of a cellmate confession, we say the judge must give a warning."

In addition to that issue Fitzgerald is also charging "serious prosecutorial misconduct." The claim stems from prosecutor Theodore Guerra's closing argument. Guerra railed at efforts by Labrador's family to wage a boycott of the British Virgin Islands and criticized the recruitment of Plante's former parole officer to testify about his unreliability. Guerra even suggested that the parole officer could have manufactured a non-notarized transcript of a 1995 hearing where Plante said a cellmate confessed in an unrelated murder case.

In a formal written response to the appeal, prosecutors noted that Labrador's trial defense lawyer did not object when Guerra informed the judge that no special caution was necessary concerning inmate testimony. The prosecution also contends in their filing that even if the judge did not caution the jury explicitly, he made it clear to the seven women and two men on the panel that the case boiled down to the word of a convicted criminal with pending charges against a defendant who denied guilt.

"The jury, by their verdict, must have been sure that [Labrador's evidence] denying the conversation with Plante could not be believed,'' prosecutors wrote. "This is not particularly surprising. Even the counsel for [Labrador] had to attempt to explain his rocking and smiling and trying to be nice in the witness box.''

At the end of the first day of Monday's hearing in London, Labrador's mother, Barbara Labrador of Long Island, was resolute as ever. "I'm not going to be satisfied until William is home,'' she said.

Before the Crown gets a chance to respond to Labrador's complaints, the committee will hear first from a lawyer for Benedetto, one of Labrador's original co-defendants.

Benedetto has technically been a fugitive from the Tortolan authorities since the Eastern Caribbean Court of Appeal ruled last year that Plante's testimony about overheard prison conversations involving Benedetto was sufficient evidence for the jury to consider his guilt or innocence. The Judicial Committee of the Privy Council will also decide whether Benedetto will have to face a retrial.