The conviction of two migrants sentenced to death for the murder of two British backpackers in Thailand has been upheld.

Wai Phyo and Zaw Lin, both from Myanmar, had denied killing David Miller and raping and killing Hannah Witheridge on the resort island of Koh Tao.

Their battered bodies were found on a beach on the morning of September 15, 2014.

Wai Phyo, centre, and Zaw Lin, right, are escorted by police officers at the Supreme Court in Bangkok, Thailand Credit: Sakchai Lalit/AP

Lawyers for the two men had claimed evidence used in the case against them was mishandled and they made confessions under duress that they later retracted, raising questions about police competence and the judicial system in Thailand.

The trial also saw a well-known Thai forensics expert testify that the DNA evidence which formed a major element of the prosecution’s case did not link the defendants to the scene.

The expert also alleged that police had failed to properly control the crime scene and mishandled the DNA evidence.

But a court rejected the defence arguments and in December 2015 convicted both defendants of murder and sentenced them to death.

Following Thursday's court hearing, Phil Robertson, Deputy Asia Director for Human Rights Watch (HRW) called on Thailand to "abolish the death penalty".

"It's a cruel and unusual punishment that violates international human rights standards," he added.

Following the initial ruling, HRW called the verdict “profoundly disturbing”, citing the defendants’ accusations of police torture that were never investigated and questionable DNA evidence linking them to the crime.

The killers have had their convictions upheld Credit: Sakchai Lalit/AP

But Thailand’s Supreme Court has now upheld their convictions.

Miss Witheridge, 23, from Norfolk, and Mr Miller, 24, from Jersey, had arrived in Thailand separately and met at the hotel where they were both staying.

Their killers, who were both 22 at the time, were employed as service workers on the island, which is famous for is diving locations.