Prime Minister David Cameron has admitted he is powerless to interfere with the Thai judicial system in the hunt for the killer of Hannah Witheridge - but spoke of his concern and said he stood ready to do what he could to help the country's police

Miss Witheridge, 23, and Jersey backpacker David Miller were murdered on the Thai island of Koh Tao last month.

Police in Thailand have insisted they have 'concrete' evidence linking two Burmese men to the murders of the Hemsby student and Mr Miller, as they denied reports the suspects had withdrawn their confessions.

The men, named in reports as bar workers Zaw Lin and Win Zaw Htun, were accused of the brutal murders of Miss Witheridge, 23, and 24-year-old Mr Miller on the island of Koh Tao in September.

The two suspects, both 21, were charged with three offences - conspiracy to murder, conspiracy to rape and robbery - after local police said the men confessed to the killings.

But reports emerged that Aung Myo Thant, a Burmese embassy official, had formally retracted their confessions amid allegations the pair were tortured.

Amnesty International called for an investigation into the allegations of police torture.

And the UK-based charity cited a lawyer from the Burmese embassy legal team who said he had been told that police had beaten the suspect and 'threatened him with electrocution'.

Embassy officials have formally asked Thai authorities to reopen the investigation into the murders of the two Britons amid claims the Burmese suspects in the case confessed to the crimes under torture.

The Burmese embassy's legal team has reportedly made the request to Thailand's ministry for legal affairs.

Mr Cameron said: 'I am very concerned about this absolutely horrific case, and my heart goes out to the families of the two people that were murdered.

He claimed he had 'acted as quickly as I could' to use the fact he was meeting the Thai leader, and said he had 'pressed him hard' to make sure that everything that could be done to find out what happened, was done, including the offer of British police and expertise.

'I am very glad that is underway and relatively quickly the police and experts were on a plane and out to Thailand to try and help,' he added.

But said: 'Obviously we can't interfere with another country's judicial system, but we should do what we can to help, and to ensure that the people who did this are found and justice is done and that is what we are focused on.'