Migrant workers Ko Zaw Lin and Ko Win Zaw Tun were charged with the murder of Mr David Miller, 24, and the rape and murder of Ms Hannah Witheridge, 23, after the tourists' battered bodies were found on the southern island of Koh Tao on 15th September.

The arrests of the pair, both in their early twenties, followed intense scrutiny of Thai authorities, which had been accused -- in criticism led by the British media -- of bungling the investigation in the days after the crime.

"The case has been fixed, my son is a scapegoat," Ko Zaw Lin's mother Ma Phyu Shwe Nu told the British broadcaster, adding he "has never done anything violent before".

Her comments come after Britain voiced concerns about the way in which Thai police had handled the probe so far and offered police support to Thai authorities.

Myanmar President U Thein Sein has also asked for a "fair" investigation, amid reports the accused were tortured into confessing.

The mother of the second suspect –Ko Win Zaw Tun -- told the BBC that news of her son's arrest had left her feeling suicidal.

"You know how much I love you. Tell them the truth, you're not guilty," said Ma Myint Thein, seen sobbing in the report.

Thailand has strongly rejected allegations of torture and defended its probe of the grisly double-murder, with junta chief and premier General Prayut Chan-O-Cha reiterating on 14th October that the case was "reliable".

Earlier in the week Thai authorities agreed to accept British and Myanmar observers to monitor the case but details of what form this would take were not provided.

Thai police have said the two Myanmar suspects confessed to the crime and their DNA matched samples taken from Ms Witheridge's body.

The murders dealt another blow to Thailand's tarnished image as a tourist haven after months of protests in Bangkok led to a coup in May and the introduction of martial law -- which has yet to be lifted.