Thai police have charged two migrant workers from Myanmar with the murder of David Miller, 24, and the rape and murder of Hannah Witheridge, 23, after the tourists' battered bodies were found on the southern island of Koh Tao on September 15.
Police have said the men confessed to the crime and their DNA matched samples taken from Witheridge's body.
But unease over the case has deepened amid reports that the suspects were tortured into confessing -- an allegation Thailand has strongly denied.
British Ambassador Mark Kent told AFP he was meeting with the Thai police, foreign ministry officials and his Myanmar counterpart, without giving further details.